Capactive load driving circuit, capacitive load driving method, and apparatus using the same

ABSTRACT

A capacitive load driving circuit ( 1 ) for charging and discharging a capacitive load ( 11 ) is provided with a voltage divider ( 5 ) for dividing a power supply voltage (VH) into a plurality of different voltages (V 1 -V 9 ), a plurality of condensers ( 2   a - i ) to which the voltages (V 1 -V 9 ) are respectively charged as terminal voltages, and a switch ( 7 ) for switching connections between the capacitive load ( 11 ) and the condensers ( 2   a - i ), the switch ( 7 ) sequentially connecting the condensers ( 2   a - i ) in an ascending order of the terminal voltages so that electrostatic energy is supplied to the capacitive load ( 11 ) when the capacitive load ( 11 ) is charged, the switch ( 7 ) sequentially connecting the condensers ( 2   a - i ) in a descending order of the terminal voltages so that electrostatic energy is collected from the capacitive load ( 11 ) when the capacitive load ( 11 ) is discharged. With this, it is possible to provide a capacitive load drive circuit having a simple circuit configuration and capable of efficiently collecting and reusing energy accumulated in the capacitive load, and a capacitive load driving method.

TECHNICAL FIELD

[0001] The present invention relates to a capacitive load drive circuitand a capacitive load driving method for driving a capacitive load; andan apparatus using the same. More specifically, the present inventionrelates to (A) a capacitive load drive circuit for driving a capacitiveload, which is provided in an image forming apparatus that uses apiezoid and an electrostatic drive electrode to jet out ink, the piezoidand the electrostatic drive electrode being capacitive loads, adischarge electrode of a plasma display, a drive circuit of a liquidcrystal display, or the like, (B) a capacitive load driving method, and(C) an apparatus using the same (in particular, apparatus that includesa capacitive load and a capacitive load drive circuit), such as an imageforming apparatus, a display apparatus, a voltage pulse generatingapparatus, and a DC-AC converter. The present invention particularlyrelates to a capacitive load drive circuit and a capacitive load drivingmethod that are capable of reducing electrical power consumption; and anapparatus using the same, such as an image forming apparatus, a displayapparatus, and a voltage pulse generating apparatus, and a DC-ACconverter.

BACKGROUND ART

[0002] Conventionally known ink-jet printers include an ink-jet printerthat uses a piezoid to jet out ink (see Patent Document 1 (JapaneseUnexamined Patent Publication No. 247051/1988, Tokukaisho 63-247051,published on Oct. 13, 1988) and Patent Document 2 (Japanese UnexaminedPatent Publication No. 10043/2001, Tokukai 2001-10043, published on Jan.16, 2001), for example), an ink-jet printer employing an electrostaticmethod, and an ink-jet printer employing a thermal method (see PatentDocument 3 (Japanese Unexamined Patent Publication No. 238245/2000,Tokukai 2000-238245, published on Sep. 5, 2000), for example).

[0003] In an ink-jet printer that uses a piezoid to jet out ink, thepiezoid is provided to a pressure generating chamber which is connectedto a nozzle orifice of an ink-jet head. In accordance with a voltageapplied as a drive signal to the piezoid which is a capacitive load, thepiezoid is caused to repeat charging and discharging, thereby jettingout ink from the nozzle orifice. Here, a capacitive load drive circuitthat drives such a capacitive load will be discussed.

[0004]FIG. 25 shows a capacitive load drive circuit employing apush-pull method, as an example of the conventional capacitive loaddrive circuit as described above. As shown in a circuit diagram of FIG.25(a), the capacitive load drive circuit is connected to a condenser CLwhich is a capacitive load. With respect to a principle voltage V whichis applied to the capacitive load drive circuit, the condenser CL isdriven under the control of a transistor Vupd provided at a charge pathfor supplying energy to the condenser CL, and a transistor Vdwndprovided at a discharge path for removing energy from the condenser CL.

[0005] FIGS. 25(b) and 25(c) are waveform charts showing waveforms ofcontrol signals for respectively controlling the operation of thetransistors Vupd and Vdwnd. When the two transistors Vupd and Vdwndoperate in response to the control signals shown in FIGS. 25(b) and25(c), a terminal voltage V0 of the condenser CL changes as time elapsesas shown in FIG. 25(d), and a current Ic flowing through a resistance Rchanges as time elapses as shown in FIG. 25(e).

[0006] Namely, in the push-pull method as shown in FIG. 25(a), thetransistor Vupd is switched ON to supply a charge current to thecapacitive load via the charge path, and then the transistor Vdwnd isswitched ON to discharge all of the electric charge to the ground viathe discharge path.

[0007] In the conventional capacitive load drive circuit, all of theelectric charge which is accumulated in the condenser CL is dischargedto the ground. In other words, all of the electrostatic energyaccumulated in the condenser CL is discarded, resulting in a problem oflarge power consumption. For example, when a frequency f of Vupd is 126kHz, a capacitance CL of the condenser CL is 0.1 μF, and a principlevoltage V is 20 V, an average power supply current is as follows.

f×CL×V=0.2520A

[0008] Accordingly, electrical power consumption is 5.04 W.

[0009] For this reason, suggested is a capacitive load drive circuitthat collects the electric charge discharged from the capacitive loadand reuses the collected electric charge to charge the capacitive load,aiming to reduce the electrical power consumption. For example, PatentDocument 4 (Japanese Unexamined Patent Publication No. 314364/1999,Tokukaihei 11-314364, published on Nov. 16, 1999) discloses a recordhead drive circuit. This record head drive circuit during printingoperation uses a discharge current discharged from the piezoid(piezoelectric vibrating element) to charge a secondary power source(secondary battery or large-capacity capacitor) by a mutual inductioneffect produced by a magnetic circuit, and reuses the electric chargeaccumulated in the secondary power source to charge the piezoid.

[0010] A further known technique is to use LC resonance to collectelectrical power in a drive circuit that drives a discharge cell of aplasma display panel (see Patent Document 5 (U.S. Pat. No. 4,866,349,published on Sep. 12, 1989)). An example of the drive circuit that usesthe LC resonance to collect electrical power from the discharge cellwill be explained with reference to FIG. 28. Note that, in FIG. 28, Cdis a capacitive component (capacitive load) of the plasma display panelwhich is the capacitive load, Css is a condenser, S1 through S4 areswitches, L is an inductor, D1 and D2 are rectifying diodes, and 2V0 isa power supply terminal which supplies a power supply voltage 2V0.

[0011] First, an initial potential V0 is initially supplied to thecondenser Css. Here, it is assumed that the potential of Cd is initially0. Further, it is assumed that a capacitance Css of the condenser Css issufficiently larger than a capacitance Cd of the capacitive load Cd.

[0012] Next, the charging and discharging operation of the capacitiveload Cd in the above arrangement will be explained with reference toFIG. 29. FIG. 29 shows changes in a terminal voltage V of the capacitiveload Cd, and states of the switches S1 through S4. Note that, theswitches S1 through S4 are turned OFF except during the periods “On” asindicated in FIG. 29.

[0013] When charging, only the switch S1 is turned ON among the switchesS1 through S4. Then, a current from the condenser Css flows into thecapacitive load Cd via the inductor L, so as to charge the capacitiveload Cd ({circle over (1)} in FIG. 29). Due to the LC resonance, thecapacitive load Cd is charged so as to have the terminal voltage V ofnot less than V0 ({circle over (2)} in FIG. 29). The rectifying diode D1prevents the inversion of current, so that the terminal voltage V of thecapacitive load Cd is clamped ({circle over (3)} in FIG. 29). Followingthis, the switch S1 is turned OFF, and then the switch S3 is turned ON.With this, the capacitive load Cd is charged to have the terminalvoltage V of 2V0 ({circle over (4)} in FIG. 29).

[0014] When discharging, the switch S3 is turned OFF, and then theswitch S2 is turned ON. With this, a current from the condenser Cd flowsinto the condenser Css via the inductor L, so as to discharge thecapacitive load Cd and charge the condenser Css ({circle over (5)} inFIG. 29). Due to the LC resonance, the capacitive load Cd is dischargedso as to have the terminal voltage V of less than V0 ({circle over (6)}in FIG. 29). The rectifying diode D2 prevents the inversion of current,so that the terminal voltage V of the capacitive load Cd is cramped({circle over (7)} in FIG. 29). Following this, the switch S2 is turnedOFF, and then the switch S4 is turned ON. With this, the capacitive loadCd is discharged to have the terminal voltage V of 0 ({circle over (8)}in FIG. 29). In this manner, this arrangement can collect electricalpower from the capacitive load Cd to the condenser Css using the LCresonance.

[0015] Further, a prior example shows that a plurality of inductors Lare selectively used in a circuit which collects electrical power usingthe LC resonance as described above (see Patent Document 6 (JapaneseUnexamined Patent Publication No. 87189/1990, Tokukaihei 2-87189,published on Mar. 28, 1990; Japanese Patent No. 2771523)).

[0016] Further, Patent Document 7 (Japanese Unexamined PatentPublication No. 170529/1999, Tokukaihei 11-170529, published on Jun. 29,1999) and Patent Document 8 (Japanese Unexamined Patent Publication No.218782/2000, Tokukai 2000-218782, published on Aug. 2, 2000) describe acircuit in which an inductor is inserted to collect energy.

[0017] Further, another known method is that, when a capacitive load isdischarged, electric charge is accumulated in a condenser and isdischarged to the ground only for an amount that exceeds theaccumulating capacity of the condenser, and when the capacitive load ischarged, the electric charge accumulated in the condenser is reused tocharge a piezoid. Only an amount of electric charge to charge up thepiezoid form the level of the electric charge thus accumulated issupplied from a power source. For example, Patent Document 9 (JapaneseUnexamined Patent Publication No. 322560/1997, Tokukaihei 9-322560,published on Dec. 12, 1997; Japanese Patent No. 3120210) discloses atechnique to reuse a part of electric charge charged to a capacitiveload in a drive circuit of a capacitive load such as an EL(electroluminescence) element. In this technique, a condenser isprovided in the drive circuit; and when the capacitive load isdischarged, only a remaining portion of the charged electric charge isdischarged after a part of the charged electric charge is sent to thecondenser, and the capacitive load starts charging after the electriccharge moved to the condenser is sent back to the capacitive load,thereby reusing a part of electric charge charged to the capacitive loadin the drive circuit of the capacitive load. As a method to collect andreuse electrostatic energy, Patent Document 9 discloses a method inwhich a condenser 263 collects and reuses electrostatic energy from acapacitive load (EL element) 261, as shown in FIG. 26.

[0018] Next, the operation of the capacitive load drive circuitdisclosed in Patent Document 9 will be concretely explained withreference to FIG. 27. Note that, to make the operation principle easilyunderstandable, a drive voltage generating circuit as described inPatent Document 9 is schematically shown with a power supply terminal VHhaving a power supply voltage VH, and ON/OFF control of the drivevoltage generating circuit as described in Patent Document 9 isschematically shown with a switch 262, in FIGS. 26 and 27.

[0019] First, the capacitive load 261 and the regenerative condenser 263are initially grounded via the switches 264 and 265 which are turned ON,as shown in FIG. 26(a). Here, the switch 262 is turned OFF so as to stopa drive voltage from being supplied from the power supply terminal VH(drive voltage generating circuit; not shown) into the capacitive load261.

[0020] Next, as shown in FIG. 27(b), the switches 264 and 265 are turnedOFF, and then the switch 262 is turned ON. Accordingly, the power supplyterminal VH outputs the power supply voltage VH to the capacitive load261 via the switch 262 which is turned ON, so as to charge thecapacitive load 261 with the power supply voltage VH from the powersupply terminal VH. This raises a terminal potential of the capacitiveload 261 so as to be equal to the power supply voltage VH.

[0021] Next, as shown in FIG. 27(c), the switch 262 is turned OFF; andthe switch 265 is turned ON. This stops the drive voltage from beingsupplied from the power supply terminal VH to the capacitive load 261;and connects one end of the capacitive load 261 with the condenser 263.As a result, a part of the electric charge charged in the capacitiveload 261 moves to the condenser 263 so that the capacitive load 261 isdischarged and the condenser 263 collects the part of electrostaticenergy accumulated in the capacitive load 261.

[0022] Next, as shown in FIG. 27(d), the switch 265 is turned OFF, andthen the switch 264 is turned ON. With this, remaining electric chargein the capacitive load 261 is discharged to the ground (power supplyterminal; not shown) via the switch 264. In other words, the remainingenergy in the capacitive load 261 is consumed via the switch 264.Namely, with this step, a voltage of the capacitive load 261 becomesequal to a ground potential.

[0023] Further, in order that the capacitive load 261 having an initialelectric charge of “0” can reuse the electrostatic energy collected inthe condenser 263, the switch 264 is turned OFF, and then the switch 265is turned ON, as shown in FIG. 27(e). With this, the electric chargecharged in the condenser 263 moves to the capacitive load 261, so thatelectrical power is fed back from the condenser 263 to the capacitiveload 261.

[0024] After this, the capacitive load 261 is driven by repeating theoperation of FIGS. 27(b) through 27(e). In this way, a part of theelectric charge emitted (discharged) from the capacitive load 261 iscollected to the condenser 263 and is sent back to the capacitive load261, so that electrical power is regenerated in the capacitive load 261.

[0025] Note that, also known are techniques to reduce electrical powerconsumption by collecting and reusing electric charge accumulated in aliquid crystal display panel (see Patent Document 10 (JapaneseUnexamined Patent Publication No. 326863/1999, Tokukaihei 11-326863,published on Nov. 26, 1999), Patent Document 11 (Japanese UnexaminedPatent Publication No. 352459/1999, Tokukaihei 11-352459, published onDec. 24, 1999), and Patent Document 12 (Japanese Unexamined PatentPublication No. 22329/2001, Tokukaihei 2001-22329, published on Jan. 26,2001)).

[0026] Further, Patent Document 13 (Japanese Unexamined PatentPublication No. 206191/1999, Tokukaihei 11-206191, published on Jul. 26,1999) discloses a motor control circuit.

[0027] However, the power regenerating circuit which uses the mutualinduction effect with respect to a magnetic circuit, as described inPatent Document 4, cannot efficiently collect and reuse theelectrostatic energy accumulated in the capacitive load because of theconversion efficiency of the mutual induction effect and the efficiencyof a charge circuit.

[0028] The record head drive circuit of Patent Document 4 uses themutual induction between inductances to generate an inducedelectromotive force from a current discharged from the piezoid, and thegenerated induced electromotive force is charged to the secondarybattery or the large-capacity condenser. With this arrangement, theelectrostatic energy can be collected and reused repeatedly. On theother hand, because of the need for the inductances, leads to acomplicated configuration, and loss of electrostatic energy due to a DCresistive component of the inductances and loss due to the efficiency ofthe mutual induction between the inductances. This results in loweredefficiency in collecting electric charge. Further, together with lossdue to the charge circuit which uses the induced electromotive force tocharge the secondary battery or the large-capacity condenser, the totalsystem has a collection efficiency of 50% at most.

[0029] The arrangements of Patent Documents 5 and 6 have problems asdescribed below.

[0030] First, the arrangement of Patent Document 5 is only applicable tousage in which a capacitance value of the capacitive load to be drivenis fixed or almost fixed. In other words, in case many piezoids in anink-jet head are driven, for example, the capacitance value of thecapacitive load widely varies depending on the number of piezoids forjetting out ink. Further, in a plasma display, the number oflight-emitting elements to be illuminated widely varies the capacitancevalue of the capacitive load in case a drive circuit drives manylight-emitting elements. In the arrangement of Patent Document 5,changes in the capacitance value of the capacitive load vary a frequencyof the LC resonance, thereby varying operation characteristics of thecircuit. When the capacitive load has a large capacitance value, inparticular, there is a possibility that the rising of the waveformdelay, thereby hindering the terminal voltage of the capacitive loadfrom rising to a predetermined voltage in a period in which the switchS1 is turned ON. This results in a lowered regeneration ratio. For thisreason, it is difficult to apply the arrangement of Patent Document 5 inorder to drive the capacitive load whose capacitance value widelychanges, such as a capacitive component of an ink-jet head using apiezoid, for example. Of course, the circuit of Patent Document 5 may beprovided to each piezoid of the ink-jet head. In this case, however, itis necessary to provide many inductors L, resulting in an extremelylarge circuit scale.

[0031] The above problems could be solved by continuously varying theinductances L of the inductors L in accordance with the changes in thecapacitance value of the capacitive load, but it is difficult tocontinuously vary the inductances L of the inductors L.

[0032] Further, the arrangement of Patent Document 6 in which theplurality of inductors L are switched over can solve the above problemsto a certain extent, but the circuit scale- accordingly becomes largebecause the plurality of inductors L are provided. Namely, thisarrangement can be applied to only a limited range of usage.

[0033] Further, the arrangements employing the inductor L (coil) havecommon problems such as a large circuit scale, difficulty in arrangingcircuits due to leak of magnetic flux, and high costs.

[0034] Further, Patent Documents 7 and 8 do not describe a technique tocollect and reuse electrostatic energy.

[0035] The capacitive load drive circuit of Patent Document 9 hasproblems such that efficiency of the condenser in collecting electriccharge is low, and thus power regeneration efficiency of the capacitiveload (ratio of regenerated electrical power to initial electrical power)is low.

[0036] Namely, in the step of FIG. 27(b), a terminal potential V (Cd) ofthe capacitive load 261 is as follows:

V(Cd)=VH

[0037] When a part of energy of the capacitive load 261 is collected bythe condenser 263 in the step 27(c), the terminal potential V (Cd) ofthe capacitive load 261 and a terminal voltage V (Cs) of the condenser263 are as follows:

V(Cd)=V(Cs)={Cd/(Cd+Cs)}VH,

[0038] where Cd is the capacitance of the capacitive load 261, and Cs isthe capacitance of the condenser 263. For example, when the capacitanceof the capacitive load 261 equals to the capacitance of the condenser263, a voltage VH/2 is supplied to the condenser 263.

[0039] The voltage V (Cd) which is supplied to the capacitive load 261in the step of FIG. 27(e) is as follows.

V(Cd)={Cd·Cs/(Cd+Cs)² }VH

[0040] For example, when the capacitance of the capacitive load 261equals to the capacitance of the condenser 263, a voltage VH/4 issupplied to the capacitive load 261. The maximum power regenerationratio can be achieved when the terminal potential V (Cd) of thecapacitive load 261 after the power regeneration is at the maximum.Here, a regeneration ratio Re of the voltage with respect to an initialvoltage VH is as follows.

Re=Cd·Cs/(Cd+Cs)²

[0041] This expression is alternatively expressed as below, using acapacitance ratio of the capacitive load 261 to the condenser 263,X=Cd/Cs.

Re=X/(1+X)²

[0042] Accordingly, the power regeneration ratio is maximum when X=1,namely when the capacitance of the capacitive load 261 equals to thecapacitance of the condenser 263.

Re=1/(1+1)²=¼

[0043] Therefore, the arrangement of Patent Document 7 theoretically hasa maximum regeneration ratio of 25%. After charging and discharging arerepeated, reusing efficiency becomes much lower than 25% due toremaining electric charge.

[0044] Note that, with the arrangements of Patent Documents 8 through10, the electric charge accumulated in the liquid crystal display panelcannot be efficiently collected and reused. Further, Patent Document 13does not describe any technique to collect and reuse electrostaticenergy.

DISCLOSURE OF INVENTION

[0045] In view of the foregoing problems, an object of the presentinvention is to provide a capacitive load drive circuit having a simplecircuit configuration and capable of efficiently collecting and reusingenergy accumulated in a capacitive load; a capacitive load drivingmethod; and an apparatus such as an image forming apparatus, which isprovided with a capacitive load and a capacitive load drive circuit andwhich consumes lower electrical power.

[0046] In order to solve the foregoing problems, a capacitive load ofthe present invention for charging and discharging a capacitive load ischaracterized by including a plurality of energy accumulating elementsfor dividedly accumulating electrostatic energy supplied from a powersource; and switching means for selectively connecting the capacitiveload and the plurality of energy accumulating elements, (A) whencharging the capacitive load, the switching means selectively connectingthe capacitive load and the plurality of energy accumulating elements sothat the plurality of energy accumulating elements sequentially supplyelectrostatic energy to the capacitive load, and (B) when dischargingthe capacitive load, the switching means selectively connecting thecapacitive load and the plurality of energy accumulating elements sothat the plurality of energy accumulating elements sequentially collectelectrostatic energy from the capacitive load.

[0047] With this arrangement, the plurality of energy accumulatingelements sequentially supply electrostatic energy to the capacitiveload, and the plurality of energy accumulating elements sequentiallycollect electrostatic energy from the capacitive load, therebycollecting and reusing energy highly efficiently. Further, the abovecapacitive load drive circuit is so arranged that the electrostaticenergy accumulated in the energy accumulating elements is directlycollected, thereby only requiring a simple circuit configuration. Withthis arrangement, it is possible to reduce energy consumed during thecycle of charging and discharging the capacitive load, and using asimple circuit it is possible to achieve the collection efficiency ofelectrical power in accordance with the number of the electrostaticenergy accumulating elements.

[0048] Further, with the arrangement, a waveform can be shaped bychanging the switching time. Thus, even when the capacitance of thecapacitive load changes, this does not affect the rate of rise (slewrate) of the total waveform, thereby achieving stable operation.

[0049] In order to solve the foregoing problems, a capacitive load drivecircuit of the present invention for charging and discharging acapacitive load is characterized by including a plurality of energyaccumulating elements to which a plurality of different initialpotentials are respectively applied; a reference potential terminal towhich either a reference power supply potential from a power source or aground potential is applied as a reference potential; and switchingmeans for selectively connecting (A) the energy accumulating elementsand the reference potential terminal with (B) the capacitive load, oneof the plurality of energy accumulating elements being a first energyaccumulating element having a first initial potential which is not 0,one of the plurality of energy accumulating elements being a secondenergy accumulating element having a second initial potential whosepolarity is the same as a polarity of the first initial potential andwhose absolute value is larger than an absolute value of the firstinitial potential, the reference potential being either (a) the groundpotential, (b) a potential which has the same polarity as the firstinitial potential supplied from the power source and which has a smallerabsolute value than the first initial potential, or (c) a potentialwhose polarity is reverse to the polarity of the first initial potentialsupplied form the power source, the switching means carrying out (i) afirst charging step of selectively connecting the capacitive load withthe reference potential terminal and then selectively connecting thecapacitive load with the first energy accumulating element so as tochange, toward the first initial potential, a terminal voltage of thecapacitive load, (ii) a second charging step of selectively connectingthe capacitive load with the second energy accumulating element so as toincrease an absolute value of the terminal voltage of the capacitiveload, and (iii) a discharging step of selectively connecting thecapacitive load with the first energy accumulating element so as todecrease the absolute value of the terminal voltage of the capacitiveload and so as to regenerate electrostatic energy to be accumulated inthe first energy accumulating element, the thus regeneratedelectrostatic energy being approximately equal to electrostatic energyas accumulated in the first energy accumulating element before the step(i), the steps (i) through (iii) being carried out in this order.Further, the capacitive load drive circuit may be so arranged that thereference potential terminal is a ground terminal having the groundpotential; the switching means is a plurality of switching elements,which are respectively provided between (A) the ground terminal and theplurality of energy accumulating elements and (B) the capacitive load,for selectively connecting (A) the ground terminal and the plurality ofenergy accumulating elements with (B) the capacitive load; and at leastthe accumulating element that has an initial potential whose absolutevalue is largest among the plurality of accumulating elements isconnected with the power source directly or indirectly (via a circuit).

[0050] In order to solve the foregoing problems, a capacitive load drivecircuit of the present invention for charging and discharging acapacitive load is characterized by including a power supply terminal towhich a power supply potential from a power source is applied; aplurality of energy accumulating elements to which a plurality ofdifferent initial potentials are respectively applied; and switchingmeans for selectively connecting (A) the energy accumulating elementsand the power supply terminal with (B) the capacitive load, one of theplurality of energy accumulating elements being a first energyaccumulating element having a first initial potential whose polarity isthe same as a polarity of the power supply potential and whose absolutevalue is smaller than an absolute value of the power supply potential,one of the plurality of energy accumulating elements being a thirdenergy accumulating element having either (a) a potential whose polarityis the same as the polarity of the first initial potential and whoseabsolute value is smaller than the absolute value of the first initialpotential, (b) a ground potential, or (c) a third initial potentialwhose polarity is reverse to the polarity of the first initialpotential, the switching means carrying out (i) a first charging step ofselectively connecting the capacitive load with the third energyaccumulating element and then selectively connecting the capacitive loadwith the first energy accumulating element so as to change, toward thefirst initial potential, a terminal voltage of the capacitive load, (ii)a second charging step of selectively connecting the capacitive loadwith the power supply terminal so as to increase an absolute value ofthe terminal voltage of the capacitive load, and (iii) a dischargingstep of selectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the step (i), the steps (i) through (iii)being carried out in this order.

[0051] In order to solve the foregoing problems, a capacitive load drivecircuit of the present invention for charging and discharging acapacitive load is characterized by including a plurality of energyaccumulating elements to which a plurality of different initialpotentials are respectively applied; and switching means for selectivelyconnecting the plurality of energy accumulating elements with thecapacitive load, one of the plurality of energy accumulating elementsbeing a first energy accumulating element having a first initialpotential which is not 0, one of the plurality of energy accumulatingelements being a second energy accumulating element whose absolute valueis larger than an absolute value of the first initial potential, one ofthe plurality of energy accumulating elements being a third energyaccumulating element having either a potential whose polarity is thesame as a polarity of the first initial potential and whose absolutevalue is smaller than the absolute value of the first initial potential,a ground potential, or a third initial potential whose polarity isreverse to the polarity of the first initial potential, the switchingmeans carrying out (i) a first charging step of selectively connectingthe capacitive load with the third energy accumulating element and thenselectively connecting the capacitive load with the first energyaccumulating element so as to change, toward the first initialpotential, a terminal voltage of the capacitive load, (ii) a secondcharging step of selectively connecting the capacitive load with thesecond energy accumulating element so as to increase an absolute valueof the terminal voltage of the capacitive load, and (iii) a dischargingstep of selectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the step (i), the steps (i) through (iii)being carried out in this order.

[0052] The capacitive load drive circuit may be arranged so as tofurther include a ground terminal having the ground potential, theswitching means being a plurality of switching elements, which arerespectively provided between (A) the ground terminal and the pluralityof energy accumulating elements and (B) the capacitive load, forselectively connecting (A) the ground terminal and the plurality ofenergy accumulating elements with (B) the capacitive load, at least theaccumulating element that has an initial potential whose absolute valueis largest among the plurality of accumulating elements being directlyor indirectly connected with the power source. Further, the capacitiveload drive circuit may be so arranged that the switching means is aplurality of switching elements, which are respectively provided betweenthe plurality of energy accumulating elements and the capacitive load,for selectively connecting the plurality of energy accumulating elementswith the capacitive load, at least the accumulating element that has aninitial potential whose absolute value is largest among the plurality ofaccumulating elements is directly or indirectly connected with the powersource.

[0053] In order to solve the foregoing problems, a capacitive load drivecircuit of the present invention for charging and discharging acapacitive load is characterized by including a power supply terminal towhich a power supply potential from a power source is applied; areference potential terminal to which either a reference power supplypotential supplied from a reference power source which is different fromthe power supply potential or a ground potential is applied as areference potential; a plurality of first energy accumulating elementsto which initial potentials are respectively applied, the initialpotentials being different from one another and being between thereference potential and the power supply potential; and switching meansfor selectively connecting (A) the reference potential terminal, theplurality of energy accumulating elements, and the power supply terminalwith (B) the capacitive load, the switching means carrying out the stepsof (1) connecting the capacitive load with the reference potentialterminal and then sequentially connecting the capacitive load with thefirst energy accumulating elements in an order of the initial potentialsfrom the initial potential closest to the reference potential, so as tochange, toward the power supply potential, a terminal voltage of thecapacitive load, (2) selectively connecting the capacitive load with thepower supply terminal so as to increase an absolute value of theterminal voltage of the capacitive load, and (3) selectively connectingthe capacitive load with the first energy accumulating elements in anorder of the initial potentials from the initial potential closest tothe power supply potential, so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelements, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating elements before the step (1), the steps (1) through (3)being carried out in this order.

[0054] With these arrangements, when decreasing the absolute value ofthe terminal voltage of the capacitive load so as to discharge thecapacitive load, it is possible to regenerate electrostatic energyaccumulated in the first energy accumulating elements to beapproximately equal to electrostatic energy as accumulated in the firstenergy accumulating elements before supplying energy to the capacitiveload. Therefore, the first energy accumulating elements do notapparently consume energy, thereby regenerating electrical power highlyefficiently.

[0055] In these arrangements, a DC power source may be connected to thefirst energy accumulating element via a resistance circuit, the DC powersource supplying energy into the first energy accumulating element so asto prevent a voltage drift of the first energy accumulating elementcaused by the charging and discharging of the capacitive load.

[0056] With this, it is possible to prevent the voltage drift, therebyimproving the electrical power regeneration ratio.

[0057] The capacitive load drive circuit that employs the DC powersource for preventing the voltage drift is preferably arranged so that adrive pulse having a predetermined cycle is applied to the capacitiveload; and a time constant determined by a resistance value of theresistance circuit and a capacitive component of the first energyaccumulating element is larger than the cycle of the drive pulse appliedto the capacitive load, by 50 times or more. Further, the capacitiveload drive circuit that employs the DC power source for preventing thevoltage drift is preferably arranged so that a drive pulse having apredetermined cycle is applied to the capacitive load; the switchingmeans carries out a charging step of selectively connecting thecapacitive load to different points so as to supply electrostatic energyto the capacitive load, the charging step being repeated in a pluralityof times within one cycle of the drive pulse; and the followingrelationship is satisfied:

3×Tp≦Rs·Cs≦6×Tp, where N=2;

3×Tp≦Rs·Cs≦7×Tp, where N=3;

3×Tp≦Rs·Cs≦8×Tp, where N=4; and

3×Tp≦Rs·Cs≦10×Tp, where N≧5,

[0058] where Cs is a capacitive component of the first energyaccumulating element, Tp is the cycle of the drive pulse applied to thecapacitive load, Rs is a resistance value of an energy supplying pathfrom the DC power source to the first energy accumulating element, and Nis the number of repeating the charging step during the cycle of thedrive pulse.

[0059] The capacitive load drive circuit as arranged above may be soarranged that (A) the capacitive load drive circuit for generating apositive pulse in which each of the energy accumulating elements has aninitial potential whose polarity is positive and (B) the capacitive loaddrive circuit for generating a negative pulse in which each of theenergy accumulating elements has an initial potential whose polarity isnegative are connected in parallel.

[0060] In this case, a terminal having a potential closest to the groundpotential consumes (A) energy supplied from the electrostatic energyaccumulating element having the highest positive initial potential (forgenerating a positive pulse), (B) energy supplied from the energysupplied from the electrostatic energy accumulating element having thelowest negative initial potential (for generating a negative pulse), and(C) energy supplied from the electrostatic energy accumulating elementhaving the lowest potential on the (−) pulse generating side.

[0061] In order to solve the foregoing problems, an apparatus of thepresent invention which includes a capacitive load and a capacitive loaddrive circuit for charging and discharging the capacitive load ischaracterized in that the capacitive load drive circuit includes a powersupply terminal to which a power supply potential is applied from apower source; a reference potential terminal to which either a referencepower supply potential supplied from the power source which is differentfrom the power supply potential, or a ground potential is applied as areference potential; an energy accumulating element to which an initialpotential between the reference potential and the power supply potentialis applied; and switching means for selectively connecting (A) thereference potential terminal, the energy accumulating element, and thepower supply terminal with (B) the capacitive load, the switching meanscarrying out (i) a first charging step of connecting the capacitive loadwith the reference potential terminal and then connecting the capacitiveload with the energy accumulating element, (ii) a second charging stepof selectively connecting the capacitive load with the power supplyterminal, and (iii) a discharging step of connecting the capacitive loadwith the energy accumulating element, the steps (i) through (iii) beingcarried out in this order, the following relationship being satisfied:

Cd/Cs≦0.164{Ts/(R·Cd)}^(0.2198), if Ts/(R·Cd)<2.5;

[0062] and

Cd/Cs≦0.2, if Ts/(R·Cd)>2.5,

[0063] where Cs is a capacitive component of the energy accumulatingelement, Cd is a capacitance of the capacitive load, Ts is a time duringwhich the energy accumulating element is kept connected to thecapacitive load, and R is a resistance value of charge and dischargepaths of the energy accumulating element with respect to the capacitiveload, the charge and discharge paths including switching means.

[0064] Further, in order to solve the foregoing problems, an apparatusof the present invention which includes a capacitive load and acapacitive load drive circuit for charging and discharging thecapacitive load is characterized in that the capacitive load drivecircuit includes a power supply terminal to which a power supplypotential is applied from a power source; a reference potential terminalto which either a reference power supply potential supplied from thepower source which is different from the power supply potential, or aground potential is applied as a reference potential; a plurality ofenergy accumulating elements to which initial potentials arerespectively applied, the initial potentials being different from oneanother and being between the reference potential and the power supplypotential; and switching means for selectively connecting (A) thereference potential terminal, the plurality of energy accumulatingelements, and the power supply terminal with (B) the capacitive load,the switching means carrying out (i) a first charging step of connectingthe capacitive load with the reference potential terminal and thensequentially connecting the capacitive load with the energy accumulatingelements in an order of the initial potentials from the initialpotential closest to the reference potential, (ii) a second chargingstep of selectively connecting the capacitive load with the power supplyterminal, and (iii) a discharging step of sequentially connecting thecapacitive load with the energy accumulating elements in an order of theinitial potentials from the initial potential closest to the powersupply potential, the steps (i) through (iii) being carried out in thisorder, the following relationship being satisfied:

Cd/Cs≦0.164{Ts/(R·Cd)}^(0.2198), if Ts/(R·Cd)<2.5;

[0065] and

Cd/Cs≦0.2, if Ts/(R·Cd)≧2.5,

[0066] where Cs is a capacitive component of the energy accumulatingelements, Cd is a capacitance of the capacitive load, Ts is a timeduring which the energy accumulating elements are kept connected to thecapacitive load, and R is a resistance value of charge and dischargepaths of the energy accumulating elements with respect to the capacitiveload, the charge and discharge paths including switching means.

[0067] With these arrangements, when decreasing the absolute value ofthe terminal voltage of the capacitive load so as to discharge thecapacitive load, it is possible to regenerate electrostatic energyaccumulated in the first energy accumulating elements to beapproximately equal to electrostatic energy as accumulated in the firstenergy accumulating elements before supplying energy to the capacitiveload. Therefore, the first energy accumulating elements do notapparently consume energy, thereby regenerating electrical power highlyefficiently.

[0068] Further, with these arrangements, the voltage of the capacitiveload reaches 90% of the final attainment voltage (final voltage attainedby the capacitive load after repeating the first through third stepsinfinitely) during the first through third steps. With this, change inthe voltages of the energy accumulating elements due to the flowing ofelectric charge from the energy accumulating elements to the capacitiveload is reduced, and the electrical power regeneration ratio ingenerating pulses is improved, thereby further reducing the electricalpower consumption. Further, change in the voltages of the energyaccumulating elements due to the generation of one pulse is reduced.This allows to generate a next pulse without correcting the voltagechange.

[0069] The apparatus of the present invention (apparatus having twostages) that employs the energy accumulating element is preferablyarranged so that the following relationship is satisfied:

SR≦V/(R·Cd)*(−0.0002y⁴+0.001y³+0.009y²−0.100y+0.386),

[0070] where Cd is the capacitance of the capacitive load, R is theresistance value of the charge and discharge paths of the energyaccumulating element with respect to the capacitive load, the charge anddischarge paths including the switching means, Ts is the time duringwhich the energy accumulating element is kept connected to thecapacitive load, V is a final attainment voltage, SR is a slew rate(rate of rise from 10% to 90%) of a waveform of a generated voltage, andy=Ts/(R·Cd).

[0071] The apparatus of the present invention (apparatus having twostages) that employs the energy accumulating element is preferablyarranged so that the following relationship is satisfied:

50(V/μsec)<V/(R·Cd)*(−0.0002y⁴+0.001y³+0.009y²−0100y+0.386),

[0072] where Cd is the capacitance of the capacitive load, R is theresistance value of the charge and discharge paths of the energyaccumulating element with respect to the capacitive load, the charge anddischarge paths including the switching means, Ts is the time duringwhich the energy accumulating element is kept connected to thecapacitive load, V is the final attainment voltage, and y=Ts/(R·Cd).

[0073] The apparatus of the present invention (apparatus having three ormore stages) that employs the plurality of energy accumulating elementsis preferably arranged so that the following relationship is satisfied:

SR<V/(R·Cd)*(0.0008y⁴−0.012y³+0.071y²−0.229y+0.414), when N=3;

SR<V/(R·Cd)*(0.0023y⁴−0.028y³+0.138y²−0.336y+0.434), where N=4; and

SR<V/(R·Cd)*(0.0026y⁴−0.032y³+0.153y²−0.356y+0.413), where N≧5,

[0074] where Cd is the capacitance of the capacitive load, R is theresistance value of the charge and discharge paths of the energyaccumulating elements with respect to the capacitive load, the chargeand discharge paths including the switching means, Ts is the time duringwhich the energy accumulating elements are kept connected to thecapacitive load, V is a final attainment voltage, N is the number oftimes each of the energy accumulating elements repeats a charging stepduring a cycle of a drive pulse, the SR is a slew rate (rate of risefrom 10% to 90%) of a waveform of a generated voltage, and y=Ts/(R·Cd).

[0075] The apparatus of the present invention (apparatus having three ormore stages) that employs the plurality of energy accumulating elementsis preferably arranged so that the following relationship is satisfied:

50(V/μsec)≦V/(R·Cd)*(0.0008y⁴−0.012y³+0.071y²−0.229y+0.414), where N=3;

50(V/μsec)<V/(R·Cd)*(0.0023y⁴−0.028y³+0.138y²−0.336y+0.434), where N=4;and

50(V/μsec)<V/(R·Cd)*(0.0026y⁴−0.032y³+0.153y²−0.356y+0.413), when N≧5,

[0076] where Cd is the capacitance of the capacitive load, R is theresistance value of the charge and discharge paths of the energyaccumulating elements with respect to the capacitive load, the chargeand discharge paths including the switching means, Ts is the time duringwhich the energy accumulating elements are kept connected to thecapacitive load, V is the final attainment voltage, N is the number oftimes each of the energy accumulating elements repeats the charging stepduring the cycle of the drive pulse, and y=Ts/(R·Cd).

[0077] With this arrangement, it is possible to stably operate the drivewaveform generating circuit by satisfying a slew rate required for awaveform to be generated with respect to the circuit parameters and thetime to keep connecting. In particular, when a high-speed slew rate isrequired as in an ink-jet printer, ink can be stably jetted out bysetting the lower limit of the slew rate to 50 (V/μsec). Therefore, withthis arrangement, it is possible to apply a pulse having a steepwaveform, thereby achieving a good response of the apparatus.

[0078] Note that, in the above inequities, the value of the right side(for example, V/(R·Cd)*(−0.0002y⁴+0.001y³+0.009y²−0.100y+0.386)) shouldbe as large as possible within a range that does not exceed the limit ofthe drive circuit, and the upper limit of the value is not particularlylimited.

[0079] An apparatus that includes the capacitive load drive circuit asarranged above and a capacitive load charged and discharged by thecapacitive load drive circuit is preferably arranged so that thecapacitive component of the energy accumulating elements is preferablylarger than the capacitance of the capacitive load, by 100 times ormore.

[0080] The energy accumulating elements to be used in the presentinvention, such as condensers, depend on the waveform of a pulse to begenerated. To obtain a pulse having a waveform whose rising edge issteep, it is preferable that the energy accumulating elements have goodfrequency characteristics (charge and discharge characteristics) (have asmall equivalent resistance R). With this, the energy accumulatingelements are switched from one stage to the next only after the voltageof the capacitive load is saturated to a certain extent, therebyachieving a pulse having a waveform whose rising edge is steep. Forexample, with an arrangement in which the ON resistance of the switchingelements connected to the energy accumulating elements is small, theequivalent resistance R can be smaller so as to improve the charge anddischarge characteristics of the energy accumulating elements.

[0081] When the capacitive component of the energy accumulating elementsis not less than the capacitance of the capacitive load by 100 times ormore, it is possible to stably operate the drive system. Further, whenthe capacitive component of the energy accumulating elements is lessthan the capacitance of the capacitive load by 100 times or more, thepotentials of the energy accumulating elements widely change due toenergy supply to the capacitive load, causing a significant decrease inthe electrical power regeneration ratio.

[0082] Note that, a “capacitive load” in the present specificationrefers to a load whose main component is a capacitance. The capacitiveload may be a piezoid (piezoelectric body) provided in an image formingapparatus, etc; an electrostatic drive electrode (electrostaticactuator) provided in an ink-jet head employing an electrostatic method;a discharge electrode of a plasma display of an image forming apparatus;a voltage applying electrode of a liquid crystal display; apiezoelectric actuator (piezoid); a condenser; an electrostatic motor;an electrostatic image forming apparatus; and the like. Further, thecapacitive load that consumes a relatively small amount of current maybe applied to a DC-AC converting apparatus, a voltage waveformgenerating apparatus, and the like.

[0083] An apparatus that employs the capacitive load and the capacitiveload drive circuit in accordance with the present invention may be soarranged that the capacitive load is an electrostatic drive electrode ora piezoid which is provided in an ink-jet head that pressurizes ink soas to jet out the ink in droplets; and the capacitive load drive circuitis a drive circuit for driving the electrostatic drive electrode or thepiezoid of the ink-jet head. With this arrangement, the apparatusgenerates a voltage pulse and simultaneously regenerates electricalpower during the cycle of generating the voltage pulse, therebyconsuming a small amount of electrical power when driving the piezoid orthe electrostatic drive electrode (electrostatic actuator). Therefore,it is possible to provide an image forming apparatus that consumes lowerelectrical power.

[0084] The energy accumulating element may be a secondary battery, acondenser, and the like.

[0085] The condenser has an internal resistance smaller than that of thesecondary battery, etc. Thus, the loss in the condenser itself issmaller than the secondary battery. Therefore, it is possible to collectand reuse electrostatic energy highly efficiently.

[0086] Further, the condenser is not much degraded even after repeatingcharging and discharging many times and thus has a long life, therebyachieving a long time use.

[0087] Further, the condenser generally has more excellent frequencycharacteristics than the secondary battery. Therefore, it is possible tocollect electrostatic energy efficiently even in driving a pulse ofabout 10 μs.

[0088] The condenser is most preferably a film condenser, a tantalumcondenser, an electric double layer condenser, a functional polymercondenser, and a ceramic condenser, which are excellent in theabove-described characteristics (degradation characteristics aftercharging and discharging, an internal impedance, and frequencycharacteristics).

[0089] On the other hand, the secondary battery requires a long time toaccumulate (charge) electrostatic energy, but can accumulate arelatively large amount of energy, thereby maintaining a voltage for along time. Thus, the secondary battery can allow the capacitive loaddrive circuit to operate for a long time without voltage supply from thepower source.

[0090] The secondary battery may be an alkaline accumulating storagebattery such as a nickel-cadmium battery, a nickel-hydrogen battery, anda silver oxide-cadmium battery, as well as a lithium secondary batterysuch as a manganese-lithium battery, a carbon-lithium battery, alithium-polymer battery, and a lithium-ion battery. Of the secondarybatteries, the lithium-ion battery is preferable because the lithium ionbattery does not have memory effects such as the nickel-cadmium batteryand the nickel-hydrogen battery, and is suitable for repeating chargingand discharging.

[0091] Further, the capacitive load drive circuit of the presentinvention may be arranged so as to further include an energy output pathwhich is connected to a part of the energy accumulating elements, theenergy output path supplying to an external element other than thecapacitive load the electrostatic energy that the energy accumulatingelement collects from the capacitive load.

[0092] With this arrangement, electrostatic energy collected to theenergy accumulating elements can be used by an external element otherthan the capacitive load from which the electrostatic energy iscollected, thereby efficiently reusing the electrostatic energycollected to the energy accumulating elements.

[0093] It is preferable that the plurality of energy accumulatingelements respectively have terminal voltages which are different fromone another; and (A) when charging the capacitive load, the switchingmeans sequentially connects the capacitive load with the energyaccumulating elements in an ascending order of absolute values of theterminal voltages and (B) when discharging the capacitive load, theswitching means sequentially connects the capacitive load with theenergy accumulating elements in a descending order of the absolutevalues of the terminal voltages.

[0094] With this arrangement, the energy accumulating elements areselectively connected sequentially in order of size of their terminalvoltages. With this, (A) the flow of energy from the energy accumulatingelements to the capacitive load when charging and (B) the flow of energyfrom the capacitive load to the energy accumulating elements whendischarging are canceled out with each other most efficiently. This alsoreduces an inrush current supplied to the energy accumulating elementsand to the capacitive load, thereby reducing energy loss. As a result,it is possible to further reduce electrical power consumption.

[0095] The capacitive load drive circuit of the present invention may beso arranged that when discharging the capacitive load, the switchingmeans grounds the capacitive load, after connecting the capacitive loadwith the energy accumulating element that has the smallest terminalvoltage.

[0096] With this arrangement, it is possible to minimize the energyconsumption because the electrical power consumption of the capacitiveload is a value determined by a potential difference between the groundpotential and the energy accumulating element that has the terminalvoltage of the smallest absolute value. Further, the electric chargeaccumulated in the energy accumulating elements can be reduced to 0before the energy accumulating elements are charged, thereby achievingthe stable repeating operation of the energy accumulating elements.

[0097] The capacitive load drive circuit of the present invention may beso arranged that when discharging the capacitive load, the switchingmeans keeps connecting the capacitive load with the energy accumulatingelement that has the terminal voltage of a smallest absolute value untilthe capacitive load starts charging, after connecting the capacitiveload with the energy accumulating element that has the terminal voltageof the smallest absolute value.

[0098] With this arrangement, the energy accumulated in the capacitiveload can be retained and is not discarded, thereby collecting andreusing almost all of the electrostatic energy accumulated in thecapacitive load. As a result, it is possible to collect and reuse theelectrostatic energy accumulated in the capacitive load. In this case,by supplying electrical power to another circuit from the energyaccumulating element that has the terminal voltage of the smallestabsolute value, it is possible to collect and reuse the electrostaticenergy efficiently while preventing the voltage drift of the energyaccumulating element that has the terminal voltage of the smallestabsolute value.

[0099] Further, the capacitive load drive circuit of the presentinvention may be arranged so as to further include voltage dividingmeans for dividing into a plurality of different voltages, the voltagesupplied from the power source and for supplying the divided voltagesrespectively to the energy accumulating elements. The voltage dividingmeans is provided as initial energy accumulating means for the energyaccumulating elements.

[0100] With this arrangement, during the cycle of generating a voltagepulse and simultaneously regenerating electrical power by charging anddischarging the capacitive load, the voltage dividing means cancompulsorily adjust the terminal voltages of the energy accumulatingelements to predetermined voltages, even when the amount of electriccharge in the energy accumulating elements is not restored to an initialvalue (value before supplying electrostatic energy) after collectingelectrostatic energy from the capacitive load, due to the loss andenergy emission at the capacitive load, etc. In particular, byappropriately selecting the capability of the voltage dividing means tocorrect voltages, the voltage dividing means does not react much duringthe cycle of generating a voltage pulse and simultaneously regeneratingelectrical power by charging and discharging the capacitive load, butcan prevent the drift during repeat of the cycle of generating a voltagepulse and simultaneously regenerating electrical power. As a result, itis possible to supply a highly stable voltage to the capacitive load,thereby achieving stable repeating operation.

[0101] Further, with this arrangement, the plurality of energyaccumulating elements can sequentially supply different voltages to thecapacitive load so as to sequentially increase the drive voltage of thecapacitive load when charging the capacitive load, whereas the pluralityof energy accumulating elements sequentially supply different voltagesto the capacitive load so as to sequentially decrease the drive voltageof the capacitive load. Therefore, it is possible to obtain a variety ofwaveforms for the drive voltage by adjusting switching timings of theswitching means.

[0102] It is more preferable that the voltage dividing means equallydivides the voltage supplied from the power source into n (n is not lessthan 2). With this, (A) the flow of energy from the energy accumulatingelements to the capacitive load when charging (B) the flow of energyfrom the capacitive load to the energy accumulating elements whendischarging are almost canceled out with each other most efficiently,and it is also possible to further reduce an inrush current supplied tothe energy accumulating elements and to the capacitive load, therebyreducing energy loss.

[0103] The capacitive load drive circuit of the present invention may beso arranged that the voltage dividing means includes a plurality ofresistors which are connected in series with respect to the powersource. With this arrangement, it is possible to realize the voltagedividing means in a simple configuration.

[0104] The capacitive load drive circuit that employs the voltagedividing means including the plurality of resistors is preferablyarranged so as to further include buffer amplification means, which isprovided between (A) the resistors and (B) the energy accumulatingelements, for amplifying a current flowing through the resistors and foroutputting a voltage that differs from an input voltage so as to adjustto predetermined voltages, the terminal voltages of the energyaccumulating elements.

[0105] With this arrangement, the buffer amplification means canaccurately adjust the terminal voltages of the energy accumulatingelements to predetermined voltages, when the voltage divided by theresistors does not become exactly equal to the predetermined voltage,namely, for example, when the amount of electric charge in the energyaccumulating elements is not restored to an initial value (value beforesupplying electrostatic energy) after collecting electrostatic energyfrom the capacitive load, due to the loss and energy emission at thecapacitive load, etc.

[0106] Further, with this arrangement, it is possible to reduce currentsflowing through the resistors, thereby reducing electrical powerconsumed by the resistors.

[0107] Note that, the buffer amplification means can be realized by anemitter follower.

[0108] The capacitive load drive circuit of the present invention may beso arranged that the voltage dividing means includes a constant voltageelement, such as a zener diode, for stabilizing the divided voltages.

[0109] With this arrangement, the constant voltage means such as a zenerdiode can accurately adjust the terminal voltages of the energyaccumulating elements to predetermined voltages, even when the amount ofelectric charge in the energy accumulating elements is not restored toan initial value (value before supplying electrostatic energy) aftercollecting electrostatic energy from the capacitive load, due to theloss and energy emission at the capacitive load, etc. As a result, it ispossible to supply a highly stable voltage to the capacitive load,thereby achieving stable repeating operation.

[0110] It is preferable that the voltage dividing means employing theconstant voltage means such as a zener diode further includes aplurality of constant voltage elements such as zener diodes connected inseries between the power source and a ground line; and a resistor isinserted between (A) the constant voltage elements such as zener diodesand (B) the power source or the ground line.

[0111] With this arrangement, even when the sum of both terminalvoltages (zener voltages in a case of zener diodes) of the constantvoltage elements such as zener diodes is not equal to the power supplyvoltage, the resistor can absorb the difference in the voltages, therebyachieving stable repeating operation at a certain voltage.

[0112] The capacitive load drive circuit of the present invention may beso arranged that the voltage dividing means employing the constantvoltage elements such as zener diodes includes a first voltage dividerand a second voltage divider connected in parallel between the powersource and a ground line; each of the first voltage divider and thesecond voltage divider includes the constant voltage elements such aszener diodes; a pull-up resistor is inserted between the constantvoltage elements such as zener diodes and the power source in the firstvoltage divider; and a pull-down resistor is inserted between theconstant voltage elements such as zener diodes and the ground line inthe second voltage divider.

[0113] With this arrangement, even when the sum of both terminalvoltages (zener voltages in a case of zener diodes) of the constantvoltage elements such as zener diodes is not equal to the power supplyvoltage, the pull-up resistor and the pull-down resistor can absorb thedifference in the voltages, thereby achieving stable repeating operationat a certain voltage.

[0114] It is preferable that a difference between the number of constantvoltage elements such as zener diodes included in the first voltagedivider and the number of constant voltage elements such as zener diodesincluded in the second voltage divider is not more than one.

[0115] With this arrangement, it is possible to further improve thestability of the terminal voltages of the energy accumulating elements,thereby achieving stable repeating operation.

[0116] The capacitive load drive circuit of the present invention thatemploys the voltage dividing means including the constant voltageelement such as a zener diode is preferably arranged so that acurrent-limit resistor which is inserted between the constant voltageelement such as a zener diode and the energy accumulating elements.

[0117] With this arrangement, the current-limit resistor appropriatelyselects the capability of the voltage dividing means to correctvoltages, so that the voltage dividing means does not react much duringthe cycle of generating a voltage pulse and simultaneously regeneratingelectrical power by charging and discharging the capacitive load, butcan prevent the drift during repeat of the cycle of generating a voltagepulse and simultaneously regenerating electrical power. Further, thecurrent-limit resistor can absorb a current suddenly flowing in and outof the capacitive load, and can limit a current flowing into theconstant voltage elements such as zener diodes, thereby reducing theworkload of the constant voltage elements such as zener diodes.

[0118] Further, it is preferable that all of the energy accumulatingelements respectively have one ends connected to the power source or theground line.

[0119] With this arrangement, the energy accumulating elements can berespectively separated so as not to interfere with one another. Thus,when a current from the capacitive load flows in and out of a particularenergy accumulating element, the voltage change of the particular energyaccumulating element does not affect the other energy accumulatingelements. Therefore, it is possible to further improve the stability ofthe terminal voltages of the energy accumulating elements, therebyachieving stable repeating operation.

[0120] Further, the capacitive load drive circuit of the presentinvention is preferably arranged so as to further include a switchingsection for controlling the supply of electrostatic energy from thepower source to the energy accumulating elements, the switching sectionsupplying electrostatic energy from the power source to the energyaccumulating elements only during a predetermined period before thecapacitive load is charged.

[0121] With this arrangement, the power source supplies electrostaticenergy to the energy accumulating elements only for a predetermineperiod. Thus, compared with a case where the power source alwayssupplies electrostatic energy to the energy accumulating elements, it ispossible to reduce electrical power consumed by the capacitive loaddrive circuit, and can particularly reduce electrical power consumed bythe resistors in the arrangement that employs the voltage dividing meansincluding the plurality of resistors connected in series with respect tothe power source.

[0122] Further, the capacitive load drive circuit of the presentinvention may be arranged so as to further include selecting means whichswitches over internal connecting states so as to selectively charge ordischarge one or some of capacitive loads.

[0123] With this arrangement, the selecting means selectively charge ordischarge one or some of the capacitive loads, thereby driving aplurality of capacitive loads at different timings.

[0124] Further, the capacitive load drive circuit that further employsthe selecting means is preferably arranged so that (A) an energysupplying path for supplying to the capacitive load the electrostaticenergy that is divided into the plurality of energy accumulatingelements and (B) an energy collecting path for collecting theelectrostatic energy from the plurality of energy accumulating elementsare separately provided; and each of the energy supplying path and theenergy collecting path includes the selecting means.

[0125] With this arrangement, by separately providing the energysupplying path (charge path) and the energy collecting path, it ispossible to simultaneously charge a part of the capacitive loads anddischarge the other part of the capacitive loads. With this, it ispossible to increase the number of operating the capacitive loads perunit time when driving many capacitive loads at different timings.Therefore, it. is possible to operate the capacitive loads at a highspeed.

[0126] Further, with this arrangement, by separately providing theenergy supplying path and the energy collecting path, it is possible toseparately optimize the charge characteristic and the dischargecharacteristic.

[0127] Further, the capacitive load drive circuit in which the energysupplying path and the energy collecting path are separately provided ispreferably arranged so as to further include rectifying means forrectifying currents of the energy supplying path and the energycollecting path.

[0128] With this arrangement, a short-circuit current does not flow in acase of delay in the ON/OFF operation of the switching means and thelike, thereby preventing the breakage of the circuit.

[0129] It is preferable that the capacitive load drive circuit is usedto drive as the capacitive load a piezoid for pressuring ink, thepiezoid being provided in an ink-jet head that jets out ink in droplets.

[0130] With this arrangement, it is possible to collect and reuse energyhighly efficiently when driving the piezoid of the ink-jet head whichgenerally consumes large electrical power, have large consumption of ahigh dielectric constant (about expε≠4300, for example) and a largecapacitance (80pF×320ch=0.0256 μF, for example), and is generally drivenat a high repeating frequency (10 kpps to 150 kpps). This especiallyachieves the effect of reducing electrical power consumption.

[0131] In order to solve the foregoing problems, an ink-jet printer ofthe present invention which includes an ink-jet head that uses a piezoidto pressurize ink so as to jet out the ink in droplets, and a drivecircuit for driving the piezoid of the ink-jet head is characterized inthat the drive circuit is one of the capacitive load drive circuits asarranged above.

[0132] With this arrangement, the plurality of energy accumulatingelements sequentially supply electrostatic energy to the piezoid, andthe plurality of energy accumulating elements sequentially collectelectrostatic energy from the piezoid, thereby collecting and reusingenergy highly efficiently. Therefore, it is possible to provide anink-jet printer that consumes lower electrical power.

[0133] An image forming apparatus that employs the capacitive load drivecircuit using the cycle of generating a voltage pulse and simultaneouslyregenerating electrical power generates a voltage pulse and regenerateselectrical power during the cycle of generating the pulse. With this,small electrical power is consumed when driving the piezoid or theelectrostatic drive electrode (electrostatic actuator). Therefore, it ispossible to provide an image forming apparatus that consumes lowerelectrical power.

[0134] A method for driving a capacitive load of the present inventionby charging and discharging the capacitive load is characterized byincluding an accumulating step of dividedly accumulating electrostaticenergy in a plurality of energy accumulating elements; a charging stepof sequentially supplying the electrostatic energy from the plurality ofenergy accumulating elements to the capacitive load so as to charge thecapacitive load; and a collecting step of discharging the capacitiveload so that the plurality of energy accumulating elements sequentiallycollect the electrostatic energy from the capacitive load.

[0135] With this method, the plurality of energy accumulating elementssequentially supply electrostatic energy to the piezoid when chargingthe capacitive load, and the plurality of energy accumulating elementssequentially collect electrostatic energy from the piezoid whendischarging the capacitive load, thereby collecting and reusing energyhighly efficiently.

[0136] In order to solve the foregoing problems, a method for driving acapacitive load of the present invention by charging and discharging thecapacitive load is characterized by including (i) a step of preparing afirst energy accumulating element having an first initial potentialwhich is not 0, a second energy accumulating element, and a referencepotential terminal to which either (a) a ground potential, (b) apotential supplied from a reference power source which has the samepolarity as the first initial potential and which has a smaller absolutevalue than the first initial potential, or (c) a potential supplied formthe reference power source whose polarity is reverse to the polarity ofthe first initial potential is applied as a reference potential; (ii) aninitial potential applying step of applying the first initial potentialto the first energy accumulating element, and applying to the secondenergy accumulating element a second initial potential which has thesame polarity as the first initial potential and which has a largerabsolute value than the first initial potential; (iii) a first chargingstep of selectively connecting the capacitive load with the referencepotential terminal and then selectively connecting the capacitive loadwith the first energy accumulating element so as to change, toward thefirst initial potential, a terminal voltage of the capacitive load; (iv)a second charging step of selectively connecting the capacitive loadwith the second energy accumulating element so as to increase anabsolute value of the terminal voltage of the capacitive load; and (v) adischarging step of selectively connecting the capacitive load with thefirst energy accumulating element so as to decrease the absolute valueof the terminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the first charging step, the steps (iii)through (v) being carried out in this order.

[0137] In order to solve the foregoing problems, a method for driving acapacitive load of the present invention by charging and discharging thecapacitive load is characterized by including (i) a step of preparing apower supply terminal to which a power supply potential is applied froma power source, a first energy accumulating element, and a third energyaccumulating element; (ii) an initial potential applying step ofapplying to the first energy accumulating element a first initialpotential which has the same polarity as the power supply potential andwhich has a smaller absolute value than the power supply potential, andapplying to the third accumulating element either a potential which hasthe same polarity as the first initial potential and which has a smallerabsolute value than the first initial potential, a ground potential, ora third initial potential whose potential is reverse to the polarity ofthe first initial potential; (iii) a first charging step of selectivelyconnecting the capacitive load with the third energy accumulatingelement and then selectively connecting the capacitive load with thefirst energy accumulating element so as to change, toward the firstinitial potential, a terminal voltage of the capacitive load; (iv) asecond charging step of selectively connecting the capacitive load withthe power supply terminal so as to increase an absolute value of theterminal voltage of the capacitive load; and (v) a discharging step ofselectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the first charging step, the steps (iii)through (v) being carried out in this order.

[0138] For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0139]FIG. 1 is a circuit diagram showing an arrangement of a capacitiveload drive circuit in accordance with an embodiment of the presentinvention.

[0140] FIGS. 2(a) through 2(c) are timing charts showing the operationof the capacitive load drive circuit of FIG. 1. FIG. 2(a) is a waveformchart of a synchronizing signal, FIG. 2(b) is a waveform chart of acontrol voltage of a transistor, and FIG. 2(c) is a waveform chart of avoltage applied to a condenser.

[0141] FIGS. 3(a) through 3(d), which show enlarged parts of the timingcharts shown in FIGS. 2(a) through 2(c), illustrate how a switchoperates. FIG. 3(a) is a waveform chart of the synchronizing signal,FIG. 3(b) is a timing chart showing how the switch operates, FIG. 3(c)is a waveform chart of the control voltage of the transistor, and FIG.3(d) is a waveform chart of the voltage applied to the condenser.

[0142]FIG. 4 is a circuit diagram showing an arrangement of a capacitiveload drive circuit in accordance with another embodiment of the presentinvention.

[0143] FIGS. 5(a) through 5(c) are timing charts showing the operationof the capacitive load drive circuit of FIG. 4. FIG. 5(a) is a waveformchart of a synchronizing signal, FIG. 5(b) is a waveform chart of acontrol voltage of a transistor, and FIG. 5(c) is a waveform chart of avoltage applied to a condenser.

[0144] FIGS. 6(a) through 6(d), which show enlarged parts of the timingcharts shown in FIGS. 5(a) through 5(c), illustrate how a switchoperates. FIG. 6(a) is a waveform chart of the synchronizing signal,FIG. 6(b) is a timing chart showing how the switch operates, FIG. 6(c)is a waveform chart of the control voltage of the transistor, and FIG.6(d) is a waveform chart of the voltage applied to the condenser.

[0145]FIG. 7 is a circuit diagram showing an arrangement of a capacitiveload drive circuit in accordance with a further embodiment of thepresent invention.

[0146]FIG. 8 is a circuit diagram showing an arrangement of a capacitiveload drive circuit in accordance with yet another embodiment of thepresent invention.

[0147] FIGS. 9(a) through 9( c) are timing charts showing the operationof the capacitive load drive circuit of FIG. 8. FIG. 9(a) is a waveformchart of a synchronizing signal, FIG. 9(b) is a waveform chart of acontrol voltage of a transistor, and FIG. 9(c) is a waveform chart of avoltage applied to a condenser.

[0148] FIGS. 10(a) through 10(d), which show enlarged parts of thetiming charts shown in FIGS. 9(a) through 9(c), illustrate how a switchoperates. FIG. 10(a) is a waveform chart of the synchronizing signal,FIG. 10(b) is a timing chart showing how the switch operates, FIG. 10(c)is a waveform chart of the control voltage of the transistor, and FIG.10(d) is a waveform chart of the voltage applied to the condenser.

[0149]FIG. 11 is a circuit diagram showing an arrangement of an emitterfollower used in a modification of the capacitive load drive circuit ofFIG. 8.

[0150]FIG. 12 is a circuit diagram showing an arrangement of an emitterfollower used in another modification of the capacitive load drivecircuit of FIG. 8.

[0151]FIG. 13 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with still anotherembodiment of the present invention.

[0152] FIGS. 14(a) through 14(c) are waveform charts showing waveformsof voltages applied to a condenser by the capacitive load drive circuitof FIG. 13. FIG. 14(a) is a waveform chart of a voltage in A phase, FIG.14(b) is a waveform chart of a voltage in B phase, and FIG. 14(c) is awaveform chart of a voltage in C phase.

[0153]FIG. 15 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with yet another embodimentof the present invention.

[0154] FIGS. 16(a) through 16(c) are waveform charts showing waveformsof voltages applied to a condenser by the capacitive load drive circuitof FIG. 15. FIG. 16(a) is a waveform chart of a voltage in A phase, FIG.16(b) is a waveform chart of a voltage in B phase, and FIG. 16(c) is awaveform chart of a voltage in C phase.

[0155]FIG. 17 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with still anotherembodiment of the present invention.

[0156] FIGS. 18(a) and 18(b) are circuit diagrams used for explainingthe operation of a voltage divider provided in the capacitive load drivecircuit of FIG. 17.

[0157]FIG. 19 is a circuit diagram showing a modification of thecapacitive load drive circuit of FIG. 17.

[0158]FIG. 20 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with yet another embodimentof the present invention.

[0159]FIG. 21 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with still anotherembodiment of the present invention.

[0160]FIG. 22 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with yet another embodimentof the present invention.

[0161]FIG. 23 is a perspective view showing chief members of an ink-jetprinter (image forming apparatus) in accordance with an embodiment ofthe present invention.

[0162]FIG. 24 is a cross-sectional view showing an arrangement of anink-jet head provided in the ink-jet printer (image forming apparatus)of FIG. 23.

[0163] FIGS. 25(a) through 25(e) are a diagram and charts showing anexample of a conventional capacitive load drive circuit. FIG. 25(a) is acircuit diagram showing an arrangement of the capacitive load drivecircuit, FIGS. 25(b) and 25(c) are waveform charts showing controlvoltages for controlling two transistors provided in the capacitive loaddrive circuit, FIG. 25(d) is a waveform chart of a terminal voltage of adriven condenser, and FIG. 25(e) is a waveform chart of a currentflowing across a resistor of the capacitive load drive circuit.

[0164]FIG. 26 is a circuit diagram showing an example of a conventionalcapacitive load drive circuit.

[0165] FIGS. 27(a) through 27(e) are circuit diagrams used forexplaining the operation of the conventional capacitive load drivecircuit of FIG. 26.

[0166]FIG. 28 is a circuit diagram showing another example of aconventional capacitive load drive circuit.

[0167]FIG. 29 is a waveform chart used for explaining the operation ofthe conventional capacitive load drive circuit of FIG. 28. FIG. 29 showsa terminal voltage of a capacitive load and states of switches.

[0168]FIG. 30 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with still anotherembodiment of the present invention.

[0169] FIGS. 31(a) through 31(e) are circuit diagrams used forexplaining the operation of the capacitive load drive circuit of FIG.30.

[0170] FIGS. 32(a) through 32(d) are circuit diagrams used forexplaining the operation of the capacitive load drive circuit of FIG.30.

[0171]FIG. 33 is a waveform chart used for explaining the operation ofthe capacitive load drive circuit of FIG. 30.

[0172]FIG. 34 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with yet another embodimentof the present invention.

[0173] FIGS. 35(a) through 35(f) are circuit diagrams used forexplaining the operation of the capacitive load drive circuit of FIG.34.

[0174]FIG. 36 is a waveform chart showing an example of a waveform of apulse generated by the capacitive load drive circuit of FIG. 34.

[0175]FIG. 37 is a waveform chart showing another example of a waveformof a pulse generated by the capacitive load drive circuit of FIG. 34.

[0176]FIG. 38 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with still anotherembodiment of the present invention.

[0177]FIG. 39 is a waveform chart showing an example of a waveform of apulse generated by the capacitive load drive circuit of FIG. 38.

[0178]FIG. 40 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with yet another embodimentof the present invention.

[0179]FIG. 41 is a waveform chart showing an example of a waveform of apulse generated by the capacitive load drive circuit of FIG. 40.

[0180]FIG. 42 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with still anotherembodiment of the present invention.

[0181]FIG. 43 is a waveform chart showing an example of a waveform of apulse generated by the capacitive load drive circuit of FIG. 42.

[0182]FIG. 44 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with yet another embodimentof the present invention.

[0183]FIG. 45 is a waveform chart showing an example of a waveform of apulse generated by the capacitive load drive circuit of FIG. 44.

[0184]FIG. 46 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with still anotherembodiment of the present invention.

[0185]FIG. 47 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with yet another embodimentof the present invention.

[0186]FIG. 48 is a waveform chart showing an example of a waveform of apulse generated by the capacitive load drive circuit of FIG. 47.

[0187]FIG. 49 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with still anotherembodiment of the present invention.

[0188]FIG. 50 is a circuit diagram used for explaining the principle ofthe present invention.

[0189] FIGS. 51(a) and 51(b) are diagrams used for explaining theprinciple of the present invention. FIG. 51(a) is a graph showing howvoltages change, and FIG. 51(b) is a graph showing how a currentchanges.

[0190]FIG. 52 is another circuit diagram used for explaining theprinciple of the present invention.

[0191]FIG. 53 is a further circuit diagram used for explaining theprinciple of the present invention.

[0192]FIG. 54 is a diagram schematically showing energy supply to acapacitive load from one condenser in the capacitive load drive circuitin accordance with the present invention.

[0193]FIG. 55 is a graph showing how the voltage of the capacitive loadchanges in accordance with the energy supply from the condenser.

[0194]FIG. 56(a) is a graph showing how the voltage of the capacitiveload changes in accordance with energy supply from one condenser, andFIG. 56(b) is a graph showing how the voltage of the capacitive loadchanges in accordance with energy supply from a plurality of condensersin the capacitive load drive circuit of the present invention. In bothFIGS. 56(a) and 56(b), a switching time (Ts) is shorter than a timeconstant (R·Cd).

[0195]FIG. 57(a) is a graph showing how the voltage of the capacitiveload changes in accordance with energy supply from one condenser, andFIG. 57(b) is a graph showing how the voltage of the capacitive loadchanges in accordance with energy supply from a plurality of condensersin the capacitive load drive circuit of the present invention. In bothFIGS. 57(a) and 57(b), a switching time (Ts) is equal to a timeconstant.

[0196]FIG. 58(a) is a graph showing how the voltage of the capacitiveload changes in accordance with energy supply from one condenser, andFIG. 58(b) is a graph showing how the voltage of the capacitive loadchanges in accordance with energy supply from a plurality of condensersin the capacitive load drive circuit of the present invention. In bothFIGS. 58(a) and 58(b), a switching time (Ts) is longer than a timeconstant.

[0197]FIG. 59 is a diagram showing a display apparatus using thecapacitive load drive circuit in accordance with an embodiment of thepresent invention.

[0198]FIG. 60 is a diagram showing a DC-AC converter using thecapacitive load drive circuit in accordance with an embodiment of thepresent invention.

[0199]FIG. 61 is a plan view showing a part of a record head which isseen from a recording medium.

[0200]FIG. 62 is a longitudinal cross-sectional view showing the recordhead.

[0201] FIGS. 63(a) through 63(c) are cross-sectional views used forexplaining the operation of the record head of FIG. 62.

[0202]FIG. 64 are pulse waveform charts used for explaining theoperation of the record head of FIG. 62.

[0203]FIG. 65 is a cross-sectional view showing an ink-jet printer(image forming apparatus) which uses the capacitive load drive circuitin accordance with another embodiment of the present invention.

[0204]FIG. 66 is a perspective view showing an ink-jet printer (imageforming apparatus) which uses the capacitive load drive circuit inaccordance with another embodiment of the present invention.

[0205]FIG. 67 is a block diagram showing a control system of the ink-jetprinter (image forming apparatus) of FIG. 65.

[0206]FIG. 68 is a diagram showing how voltages of the energyaccumulating elements change in the capacitive load drive circuit inaccordance with an embodiment of the present invention, when repeatedlycharging and discharging the capacitive load.

[0207]FIG. 69 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with yet another embodimentof the present invention.

[0208] FIGS. 70(a) through 70(c) are timing charts showing an operationexample of the capacitive load drive circuit of FIG. 69. FIG. 70(a) is awaveform chart of a synchronizing signal, FIG. 70(b) is a waveform chartof a control voltage of a switch, and FIG. 70(c) is a waveform chart ofa voltage applied to a condenser.

[0209]FIG. 71(a) through 71(d) are timing charts showing anotheroperation example of the capacitive load drive circuit of FIG. 69. FIG.71(a) is a waveform chart of the synchronizing signal, FIG. 71(b) is atiming chart showing how the switch operates, FIG. 71(c) is a waveformchart of the control voltage of the switch (switching means), and FIG.71(d) is a waveform chart of the voltage applied to the condenser.

[0210]FIG. 72 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with still anotherembodiment of the. present invention.

[0211] FIGS. 73(a) through 73(c) are timing charts showing an operationexample of the capacitive load drive circuit of FIG. 72. FIG. 73(a) is awaveform chart of a synchronizing signal, FIG. 73(b) is a waveform chartof a control voltage of a switch, and FIG. 73(c) is a waveform chart ofa voltage applied to a condenser.

[0212] FIGS. 74(a) through 74(d) are timing charts showing anotheroperation example of the capacitive load drive circuit of FIG. 72. FIG.74(a) is a waveform chart of the synchronizing signal, FIG. 74(b) is atiming chart showing how the switch (switching means) operates, FIG.74(c) is a waveform chart of the control voltage of the switch, and FIG.74(d) is a waveform chart of the voltage applied to the condenser.

[0213]FIG. 75 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with yet another embodimentof the present invention.

[0214] FIGS. 76(a) and 76(b) are circuit diagrams showing an arrangementof a capacitive load drive circuit in accordance with still anotherembodiment of the present invention.

[0215]FIG. 77 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with yet another embodimentof the present invention.

[0216]FIG. 78 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with still anotherembodiment of the present invention.

[0217]FIG. 79 is a circuit diagram showing an arrangement of acapacitive load drive circuit in accordance with yet another embodimentof the present invention.

[0218] FIGS. 80(a) and 80(b) are circuit diagrams used for explainingthe operation of a voltage divider provided in the capacitive load drivecircuit of FIG. 79.

[0219]FIG. 81 is a flow chart showing a method for driving a capacitiveload in accordance with an embodiment of the present invention.

[0220]FIG. 82 is a graph showing a maximum load capacitance ratio thatcauses a voltage of the capacitive load to be not less than 90% of anattainment voltage during first through third steps, with respect to aratio of a time constant to a switching time, in the capacitive loaddrive circuit of FIG. 30.

[0221]FIG. 83 is a graph showing how an energy consumption ratio changeswith respect to the ratio of the time constant to the switching timewhen the load capacitance ratio varies from 0.003 to 0.3 in a capacitiveload drive circuit having two stages, which is different from thecapacitive load drive circuit of FIG. 30 having four stages only in thenumber of stages.

[0222]FIG. 84 is a graph showing how an energy consumption ratio changeswith respect to the ratio of the time constant to the switching timewhen the load capacitance ratio varies from 0.003 to 0.3 in a capacitiveload drive circuit having three stages, which is different from thecapacitive load drive circuit of FIG. 30 having four stages only in thenumber of stages.

[0223]FIG. 85 is a graph showing how an energy consumption ratio changeswith respect to the ratio of the time constant to the switching timewhen the load capacitance ratio varies from 0.003 to 0.3 in thecapacitive load drive circuit of FIG. 30 having four stages.

[0224]FIG. 86 is a graph showing how an energy consumption ratio changeswith respect to the ratio of the time constant to the switching timewhen the load capacitance ratio varies from 0.003 to 0.3 in a capacitiveload drive circuit having five stages, which is different from thecapacitive load drive circuit of FIG. 30 having four stages only in thenumber of stages.

[0225]FIG. 87 is a graph showing how an energy consumption ratio changeswith respect to the ratio of the time constant to the switching timewhen the load capacitance ratio varies from 0.003 to 0.3 in a capacitiveload drive circuit having six stages, which is different from thecapacitive load drive circuit of FIG. 30 having four stages only in thenumber of stages.

[0226]FIG. 88 is a graph showing how a slew rate (10% to 90%) changeswith respect to the ratio of the time constant to the switching timewhen the load capacitance ratio X varies from 0.001 to 0.1 in acapacitive load drive circuit having two stages, which is different fromthe capacitive load drive circuit of FIG. 30 having four stages only inthe number of stages.

[0227]FIG. 89 is a graph showing how a slew rate (10% to 90%) changeswith respect to the ratio of the time constant to the switching timewhen the load capacitance ratio X varies from 0.001 to 0.1 in acapacitive load drive circuit having three stages, which is differentfrom the capacitive load drive circuit of FIG. 30 having four stagesonly in the number of stages.

[0228]FIG. 90 is a graph showing how a slew rate (10% to 90%) changeswith respect to the ratio of the time constant to the switching timewhen the load capacitance ratio varies from 0.001 to 0.3 in thecapacitive load drive circuit of FIG. 30 having four stages.

[0229]FIG. 91 is a graph showing how a slew rate (10% to 90%) changeswith respect to the ratio of the time constant to the switching timewhen the load capacitance ratio X varies from 0.003 to 0.3 in acapacitive load drive circuit having five stages, which is differentfrom the capacitive load drive circuit of FIG. 30 having four stagesonly in the number of stages.

[0230]FIG. 92 is a graph showing how a slew rate (10% to 90%) changeswith respect to the ratio of the time constant to the switching timewhen the load capacitance ratio X varies from 0.003 to 0.3 in acapacitive load drive circuit having six stages, which is different fromthe capacitive load drive circuit of FIG. 30 having four stages only inthe number of stages.

BEST MODE FOR CARRYING OUT THE INVENTION

[0231] [EMBODIMENT 1]

[0232] The following will explain one embodiment of the presentinvention with reference to FIGS. 1, 2(a) to 2(c), and 3(a) to 3(d).

[0233] As shown in FIG. 1, a capacitive load drive circuit 1 of thepresent embodiment is provided with an accumulating device 3 includingnine condensers (energy accumulating elements) 2, a voltage divider(voltage dividing means) 5 including ten resistors 4, a transistor(switching section) 6, a switch (switching means) 7, a resistor 8, and apower supply terminal 9. The capacitive load drive circuit 1 of thepresent embodiment applies a voltage V to a condenser 11 which is acapacitive load, so as to charge and discharge the condenser 11.

[0234] Via the power supply terminal 9, the capacitive load drivecircuit 1 is supplied with a power supply voltage VH from a main powersource (not shown) provided outside the capacitive load drive circuit 1.The power supply voltage VH supplied through the power supply terminal 9is applied to the voltage divider 5 via the transistor 6.

[0235] The transistor 6 is a switch for connecting/disconnecting thepower supply terminal 9 and the voltage divider 5 in response to acontrol voltage Q. In the present embodiment, the transistor 6 is a PNPtype transistor having a emitter connected to the power supply terminal9, a collector connected to the voltage divider 5, and a base to whichthe control voltage Q is applied. The transistor 6 is always switched ONwhen the capacitive load drive circuit 1 is driven. Thus, the capacitiveload drive circuit 1 may be arranged without using the transistor 6 sothat the power supply terminal 9 is directly connected to the voltagedivider 5.

[0236] Using the ten resistors 4, the voltage divider 5 divides thepower supply voltage VH which is supplied from the external main powersource. The voltage divider 5 is so arranged that the ten resistors 4are directly connected between the power supply terminal 9 and theground (reference point of potential for the power supply voltage;typically the point at which the potential is 0). These resistors 4divide the power supply voltage VH, which is supplied from the externalmain power source, into voltages V1 through V9 which are different fromone another. Namely, when the transistor 6 is switched ON to supply apositive power supply voltage VH to the voltage divider 5 (hereinafterreferred to as “when electrical power is supplied”), nine connectionpoints a, b, c, d, e, f, g, h, and i between the resistors 4respectively have voltages V1, V2, V3, V4, V5, V6, V7, V8, and V9 (where0<V1<V2<V3<V4<V5<V6<V7<V8<V9<VH). More specifically, the voltages V1through V9 are expressed as VH·R2/(R1 +R2), where R1 is a sum ofresistance values of the resistors 4 provided between the power supplyterminal 9 and the connection point having the voltage in question, andR2 is a sum of resistance values of the resistors 4 provided between theground and the connection point having the voltage in question. In thepresent embodiment, each resistor 4 is a resistive element having thesame resistance value. Accordingly, the voltages V1 through V9 in thepresent embodiment are expressed as follows: V1=VH/10, V2=2VH/10,V3=3VH/10, V4=4VH/10, V5=5VH/10, V6=6VH/10, V7=7VH/10, V8=8VH/10, andV9=9VH/10.

[0237] The accumulating device 3 is composed of nine condensers 2 athrough 2 i connected in parallel between the ground and the voltagedivider 5. Further, the condensers 2 a, 2 b, 2 c, 2 d, 2 e, 2 f, 2 g, 2h, and 2 i are respectively connected to the connection points a, b, c,d, e, f, g, h, and i. Accordingly, the voltages V1, V2, V3, V4, V5, V6,V7, V8, and V9, which are prepared by dividing the power supply voltageVH using the voltage divider 5, are respectively applied to thecondensers 2 a, 2 b, 2 c, 2 d, 2 e, 2 f, 2 g, 2 h, and 2 i as terminalvoltages (voltages of terminals connected to the switch 7), whenelectrical power is supplied.

[0238] In this way, the terminal voltages of the condensers 2 a through2 i of the accumulating device 3 are adjusted to the predeterminedvoltages V1 through V9, respectively, by the voltage divider 5. As aresult, the different terminal voltages V1 through V9 are respectivelydistributed to the condensers 2 a through 2 i. With this, the condensers2 a, 2 b, 2 c, 2 d, 2 e, 2 f, 2 g, 2 h, and 2 i accumulate electriccharge (electrostatic energy) corresponding to the voltages V1, V2, V3,V4, V5, V6, V7, V8, and V9, respectively, when electrical power issupplied.

[0239] In the present embodiment, the condensers 2 a through 2 i havethe same capacitance (electrostatic capacitance) C which is sufficientlylarger than a capacitance CL of the condenser 11. Accordingly, theelectric charge accumulated in the condensers 2 a, 2 b, 2 c, 2 d, 2 e, 2f, 2 g, 2 h, and 2 i are C·V1, C·V2, C·V3, C·V4, C·V5, C·V6, C·V7, C·V8,and C·V9, respectively.

[0240] Note that, the capacitance C of the condensers 2 a through 2 i ispreferably larger than the capacitance CL of the condenser 11 by 100times or more, so as to improve collection efficiency of electrostaticenergy.

[0241] The accumulating device 3 and the voltage divider 5 are connectedto the condenser 11 via the switch 7 and the resistor 8. The switch 7has eleven contact points T0 through T10, and selectively connects oneof the contact points T0 through T10 with an output terminal (terminalconnected to the resistor 8). Among the eleven contact points T0 throughT10, the contact point T0 is grounded; the contact points T1, T2, T3,T4, T5, T6, T7, T8, and T9 are respectively connected to the condensers2 a, 2 b, 2 c, 2 d, 2 e, 2 f, 2 g, 2 h, and 2 i; and T10 is connected tothe power supply terminal 9. Accordingly, the voltages V1, V2, V3, V4,V5, V6, V7, V8, and V9 are respectively applied to the contact pointsT0, T1, T2, T3, T4, T5, T6, T7, T8, T9, and T10, when the condenser 11is driven.

[0242] The switch 7 is switched to the contact point T0 in an initialstate (state before driving operation starts). During the drivingoperation, the switch 7 repeats an operation of sequentially switchingthe contact points from the contact point T0 through the contact pointT10 and then from the contact point T10 through the contact point T0.Further, the switch 7 receives a synchronizing signal SYNC forpulse-driving the condenser 11 from a synchronizing signal source (notshown), and carries out the operation of switching the contact pointsfrom T0 through T10 in synchronism with the synchronizing signal SYNC.Note that, the synchronizing signal SYNC and timing for switching thecontact points T0 through T10 will be detailed later.

[0243] The resistor 8 limits a current flowing into the condenser(capacitive load) 11. When the switch 7 is a semiconductor switch, theresistor 8 is inserted equivalently as an ON resistance of thesemiconductor switch.

[0244] Next, the operation of the capacitive load drive circuit 1 willbe explained with reference to FIGS. 2 and 3. Note that, it is assumedhere in the following explanation that VH is a positive voltage.

[0245] FIGS. 2(a) through 2(c) are timing charts showing the operationof the capacitive load drive circuit 1. FIG. 2(a) is a waveform chartshowing a waveform of the synchronizing signal SYNC which is supplied tothe switch 7. FIG. 2(b) is a waveform chart showing a waveform of thecontrol voltage Q of the transistor 6, which controls the operation ofthe transistor 6. FIG. 2(c) is a waveform chart showing a waveform ofthe voltage V which is applied to the condenser 11.

[0246] FIGS. 3(a) through 3(d), which show enlarged parts of the timingcharts shown in FIGS. 2(a) through 2(c), illustrate how the switch 7operates. FIG. 3(a) is an enlarged waveform chart showing a part of thewaveform of the synchronizing signal SYNC shown in FIG. 2(a). FIG. 3(b)is a timing chart showing how the switch 7 of FIG. 1 operates, namely,which one of the contact points T0 through T10 is connected to theswitch 7. FIG. 3(c) is an enlarged waveform chart showing a part of thewaveform of the control voltage Q shown in FIG. 2(b). FIG. 3(d) is anenlarged waveform chart showing a part of the waveform of the voltage Vshown in FIG. 29(c).

[0247] First, in preparatory operation before starting the drivingoperation of the condenser 11, the control voltage Q becomes a highlevel as shown in FIG. 2(b), so as to switch ON the transistor 6. Withthis, the different predetermined voltages V1 through V9, which are theexternal power supply voltage VH divided by the voltage divider 5, areapplied to the condensers 2 a through 2 i of the accumulating device 3as terminal voltages, so as to charge the condensers 2 a through 2 i. Inthe present embodiment, the transistor 6 is kept switched ON until thecondenser 11 finishes the driving operation. Here, the switch 7 isswitched to the contact point T0 so as to ground the condenser 11.

[0248] After the preparation in which the terminal voltages of thecondensers 2 a through 2 i are adjusted to the predetermined voltages V1through V9, the synchronizing signal SYNC is activated as shown in FIG.2(a), so as to start the driving operation. Here, a period to between atime point when the transistor 6 is switched ON (preparatory operationstarting point) and a time point when the synchronizing signal SYNC isactivated (driving operation starting point) is preferably set to be notless than 2.5 times a time constant of charging, so as to fully chargethe condensers 2 a through 2 i.

[0249] Then, by sequentially switching the switch 7 from the contactpoint T0 through the contact point T10 in synchronism with thesynchronizing signal SYNC, the plurality of different voltages V1 to V9and VH are applied to the condenser 11 as the voltage V. With this, apulse voltage stepping up and down in an approximately trapezoidal shapeis applied to the condenser 11 as the voltage V, as shown in FIGS. 2(c)and 3(c).

[0250] Next, the driving operation of the condenser 11 will be explainedin detail. Here, the synchronizing signal SYNC is a pulse signal havinga regular cycle T and a pulse width t, as shown in FIG. 3(a). Forexample, the cycle T is set to 8 μs, and the pulse width t is set to0.32 μm.

[0251] When driving the condenser 11, the switch 7 is switched from thecontact point T0 to the contact point T1 in synchronism with rising ofthe synchronizing signal SYNC. When the switch 7 is switched to thecontact point T1, the condenser 2 a of the accumulating device 3 isconnected to the condenser 11. Here, the terminal voltage of thecondenser 2 a is V1, whereas the terminal voltage of the condenser 11 isthe ground potential. As a result, electrostatic energy (electriccharge) is supplied from the condenser 2 a to the condenser 11, so as tocharge the condenser 11.

[0252] Here, the electric charge accumulated in the condenser 2 a isC·V1. If it is assumed that the condenser 11 receives electric chargeonly from the condenser 2 a, the voltage V applied to the condenser 11is expressed as follows:

V=C·V1/(C+CL),

[0253] where CL is a capacitance of the condenser 11. Further, it can beassumed that the voltage V is approximately equal to the predeterminedvoltage V1 generated by the voltage divider 5, because the capacitance Cof the condenser 2 a is sufficiently larger than the capacitance CL ofthe condenser 11. Accordingly, the condenser 2 a applies the voltage V1to the condenser 11 by switching the switch 7 from the contact point T0to the contact point T1.

[0254] After this, the switch 7 is switched from the contact point T1 tothe contact point T2, from the contact point T2 to the contact point T3,from the contact point T3 to the contact point T4, from the contactpoint T4 to the contact point T5, from the contact point T5 to thecontact point T6, from the contact point T6 to the contact point T7,from the contact point T7 to the contact point T8, and from the contactpoint T8 to the contact point T9. By switching the switch 7 in thismanner, the condenser 11 is sequentially connected to the condensers 2 bthrough 2 i in the ascending order of their terminal voltages. Inaccordance with this, the condensers 2 b through 2 i sequentially supplyelectrostatic energy to the condenser 11, so as to apply the voltages V2through V9 to the condenser 11 in the ascending order of the voltages,respectively in the same manner that the switch 7 is switched from thecontact point T0 to the contact point T1. As a result, the voltage V ofthe condenser 11 rises to the voltage V9.

[0255] Next, when the switch 7 is switched from the contact point T9 tothe contact point T10, the condenser 11 is connected to the power supplyterminal 9, so that the voltage V applied to the condenser 11 becomesequal to the power supply voltage VH supplied from the outside.

[0256] In this way, the voltage V of the condenser 11 rises from 0 tothe power supply voltage VH in an approximately stepped-up manner, asshown in FIG. 3(d).

[0257] Next, the switch 7 is kept switched to the contact point T10 soas to hold the voltage V. of the condenser 11 at the power supplyvoltage VH, then the switch 7 is switched from the contact point T10 tothe contact point T9. This connects the condenser 2 i of theaccumulating device 3 to the condenser 11.

[0258] Here, the electric charge accumulated in the condenser 2 i isC·V9. If it is assumed that the condenser 2 i receives electric chargeonly from the condenser 11, the voltage V applied to the condenser 11 isexpressed as follows.

V=(CL·VH+C·V9)/(C+CL)

[0259] Further, the voltage V approximately equals to the voltage V9because the capacitance C of the condenser 2 i is sufficiently largerthan the capacitance CL of the condenser 11. Accordingly, the condenser11 is connected to the condenser 2 i by switching the switch 7 from thecontact point T10 to the contact point T9. As a result, the voltage V ofthe condenser 11 drops to the predetermined voltage V9 which is adjustedby the voltage divider 5, as shown in FIG. 3(d).

[0260] Here, the condenser 2 i supplies energy to the condenser 11during the step of connecting the condenser 11 to the condenser 2 iafter the condenser 11 is connected to the condenser 2 h. Thus, if theaccumulating device 3 does not receive energy from any circuit otherthan the condenser 11 between rising and falling edges of the voltagepulse, strictly speaking, the terminal voltage of the condenser 2 i isnot V9 but slightly smaller than V9 just before the condenser 11 isconnected to the condenser 2 i after the condenser 11 is connected tothe power supply terminal 9.

[0261] However, when the condenser 2 i having the terminal voltageslightly smaller than V9 is connected to the condenser 11 which ischarged to have the power supply voltage VH, the condenser 2 i collectselectrostatic energy (electric charge) from the condenser 11 and causesthe condenser 11 to discharge, because the terminal voltage of thecondenser 11, which is now the power supply voltage VH, is larger thanthe terminal voltage of the condenser 2 i. Here, the voltage of thecondenser 2 i is restored (regenerated) to a value approximately equalto V9 (value assumable to V9) by collecting energy from the condenser11.

[0262] After this, the switch 7 is switched from the contact point T9 tothe contact point T8, from the contact point T8 to the contact point T7,from the contact point T7 to the contact point T6, from the contactpoint T6 to the contact point T5, from the contact point T5 to thecontact point T4, from the contact point T4 to the contact point T3,from the contact point T3 to the contact point T2, and from the contactpoint T2 to the contact point T1. By switching the switch 7 in thismanner, the condenser 11 is connected to the condensers 2 a through 2 hin the descending order of their terminal voltages. In accordance withthis, the condensers 2 a through 2 h sequentially collect energy fromthe condenser 11, and the voltages V1 through V8 are applied to thecondenser 11 in the descending order of the voltages, respectively inthe same manner that the switch 7 is switched from the contact point T10to the contact point T9.

[0263] Finally, when the switch 7 is switched from the contact point T1to the contact point T0, the condenser 11 is grounded so that thevoltage V applied to the condenser 11 becomes 0, which is equal to theground. The voltage V is set to 0 here so as to reduce the electriccharge accumulated in the condenser 11 to 0 for stable repeatingoperation.

[0264] In the manner described above, the voltage V of the condenser 11drops from the power supply voltage VH to 0 in an approximatelystepped-down manner, as shown in FIG. 3(d).

[0265] Note that, at the last step-down of the switch 7 (switching fromthe contact point T1 to the contact point T0), the electric chargeaccumulated in the condenser 11 is not sent back to the condensers 2 athrough 2 i and are all discarded to the ground. This means that part ofelectrostatic energy accumulated in the condenser 11 is discarded. Inthe present embodiment, the voltage V which is applied to the condenser11 is a maximum of VH, and the voltage V of the condenser 11 at the laststep-down of the switch 7 is V1, which equals to VH/10. Hence, theelectric charge accumulated in the condenser 11 is CL·VH, and theelectric charge which is discharged from the condenser 11 at the laststep-down of the switch 7 is CL·VH/10. Accordingly, if the accumulatingdevice 3 does not receive energy from any circuit other than thecondenser 11 between rising and falling edges of the voltage pulse, andthe condensers 2 a through 2 i collect all electric charge that isdischarged from the condenser 11 except the electric charge at the laststep-down of the switch 7, electric charge that the condensers 2 athrough 2 i collect from the condenser 11 is 9CL·VH/10. Namely, thecollection efficiency of electrostatic energy is {fraction (9/10)}=90%.

[0266] In this way, the applied voltage V of the condenser 11 is steppedup by sequentially switching the switch 7 from the contact point T0through the contact point T10, and then stepped down by sequentiallyswitching the switch 7 from the contact point T10 through the contactpoint T0. With this, the condensers 2 a through 2 i of the accumulatingdevice 3 can supply electrostatic energy to the condenser 11, and cancollect most of the electrostatic energy thus accumulated in thecondenser 11.

[0267] As described above, the capacitive load drive circuit 1 of thepresent embodiment is so arranged that a voltage of the main powersource is divided into n and then accumulated in the accumulating device3; and the accumulating device 3 supplies electrostatic energy to thecondenser 11 and collects electrostatic energy that is discharged fromthe condenser 11 by switching the connection between the accumulatingdevice 3 and the condenser 11. This realizes highly efficient collectionand reusing of energy.

[0268] Note that, in the capacitive load drive circuit 1 of the presentembodiment, the transistor 6 is always switched ON when the capacitiveload drive circuit 1 is driven. However, the transistor 6 may bearranged, as in Embodiment 4 to be described later, that the transistor6 is switched ON only during a predetermined period between drivingperiods, so as to supply a power supply voltage to the voltage divider5; and the transistor 6 is switched OFF when the voltage divider 5 neednot receive electrical power, so as to disconnect the voltage divider 5and the main power source. This can eliminate waste of electrical powerconsumption due to a current constantly flowing through the voltagedivider 5.

[0269] Further, the capacitive load drive circuit 1 of the presentembodiment is so arranged that the power supply terminal 9 is directlyconnected to the contact point T10 of the switch 7, but the capacitiveload drive circuit 1 may be so arranged that the power supply terminal 9is connected to the contact point T10 of the switch 7 via the transistor6.

[0270] [EMBODIMENT 1A]

[0271] The following will explain another embodiment of the presentinvention with reference to FIGS. 69, 70(a) to 70(c), and 71(a) to71(d). Note that, for convenience, members having the same functions asthose used in Embodiment 1 will be given the same reference symbols, andexplanation thereof will be omitted here.

[0272] A capacitive load drive circuit of the present embodiment has thesame arrangement as the capacitive load drive circuit 1 of Embodiment 1except the following differences.

[0273] As a first difference, switches SW1 through SW9 are respectivelyprovided between (i) nine connection points (voltage dividing points) athrough i of the voltage divider 5 and (ii) lines that respectivelyconnect to the contact points T1 through T9 in a capacitive load drivecircuit 1A of the present embodiment, as shown in FIG. 69; whereas thenine connection points (voltage dividing points) a through i of thevoltage divider 5 are directly connected to the lines that respectivelyconnect to the contact points T1 through T9 in the capacitive load drivecircuit 1 of Embodiment 1. The switches SW1 through SW9 are switchingsections for controlling the voltage supply from the voltage divider 5to the condensers 2 a through 2 i of the accumulating device 3. Theswitches SW1 through SW9 are switched ON only during a predeterminedperiod before the condenser 11 is charged.

[0274] As a second difference, the capacitive load drive circuit 1 ofEmbodiment 1 is provided with the transistor 6, and operates inaccordance with the timing charts shown in FIGS. 2(a) to 2(c), and 3(a)to 3(d), but the capacitive load drive circuit 1A is provided with aswitch 16A, instead of the transistor 6, whose operation is controlledby a control voltage Q shown in timing charts 70(a) to 70(c), or 71(a)to 71(d).

[0275] Namely, unlike the transistor 6 of Embodiment 1, the switch 16Ais switched ON for a predetermined period to before the condenser 11starts charging (here, the condenser 11 is connected to the contactpoint T0 of the switch 7 and thus grounded), as shown in FIGS. 70(a)through 70(c). Note that, the operation of the switches SW1 through SW9is controlled by a control voltage similar to the control voltage Q ofthe switch 16A.

[0276] In Embodiment 1, the accumulating device 3 is always connected tothe voltage divider 5, and a power supply voltage is always supplied tothe voltage divider 5 when the capacitive load drive circuit is driven.Accordingly, energy is supplied from another circuit to the accumulatingdevice 3 between the rising and falling edges of the voltage pulse. Thisenergy supply may decrease efficiency of the accumulating device 3 incollecting energy from the condenser 11.

[0277] In contrast, energy is not supplied from another circuit to theaccumulating device 3 between rising and falling edges of the voltagepulse in the present embodiment, as a result of the foregoing first andsecond differences. This can prevent lowering of efficiency of theaccumulating device 3 in collecting energy from the condenser 11, thelowering caused by the energy supply from the other circuit.

[0278] Next, the driving operation of the condenser 11 in the capacitiveload drive circuit 1A will be explained with reference to FIGS. 70(a) to70(c) and FIGS. 71(a) to 71(d). Here, the synchronizing signal SYNC is apulse signal having a regular cycle T and a pulse width t, as shown inFIG. 70(a). For example, the cycle T is set to 8 μs, and the pulse widtht is set to 0.32 μs. Note that, it is assumed here in the followingexplanation that VH is a positive voltage.

[0279] FIGS. 70(a) through 70(c) are timing charts showing an-operationexample of the capacitive load drive circuit 1A. FIG. 70(a) is awaveform chart showing a waveform of the synchronizing signal SYNC whichis supplied to the switch 7. FIG. 70(b) is a waveform chart showing awaveform of the control voltage Q which controls the operation of theswitch 16A. FIG. 70(c) is a waveform chart showing a waveform of thevoltage V which is applied to the condenser 11.

[0280] FIGS. 71(a) through 71(d) show another operation example of thecapacitive load drive circuit 1A. FIG. 71(a) is an enlarged waveformchart showing a part of the waveform of the synchronizing signal SYNCshown in FIG. 70(a). FIG. 71(b) is a timing chart showing how the switch7 of FIG. 1 operates, namely, which one of the contact points T0 throughT10 is connected. FIG. 71(c) is an enlarged waveform chart showing apart of the waveform of the control voltage Q which controls theoperation of the switch 16A. FIG. 71(d) is an enlarged waveform chartshowing a part of the waveform of the voltage V shown in FIG. 70(c).

[0281] In both the operation example of FIGS. 70(a) through 70(c) andthe operation example of FIGS. 71(a) through 71(d), the control voltageQ is turned ON when a pulse is not applied to the condenser 11, butcycles for turning ON the control voltage Q are different from eachother. Specifically, the control voltage Q is turned ON every few pulsesin the operation example of FIGS. 70(a) through 70(c), whereas thecontrol voltage Q is turned ON every pulse in the operation example ofFIGS. 71(a) through 71(d). When an amount of voltage drift is small, theswitch 16A may be turned ON (connection state) per few pulses to performnormalization (correction of the terminal voltages of the condensers 2 athrough 2 i), as shown in FIGS. 70(a) through 70(c). When an amount ofvoltage drift is large, the switch 16A may be turned ON (connectionstate) per each pulse to perform normalization, as shown in FIGS. 71(a)through 71(d), in order to secure stable operation.

[0282] When the condenser 11 is driven, first, the switch 7 is switchedfrom the contact point T0 to the contact point T1, from the contactpoint T1 to the contact point T2, from the contact point T2 to thecontact point T3, from the contact point T3 to the contact point T4,from the contact point T4 to the contact point T5, from the contactpoint T5 to the contact point T6, from the contact point T6 to thecontact point T7, from the contact point T7 to the contact point T8, andfrom the contact point T8 to the contact point T9, as in Embodiment 1.By switching the switch 7 in this manner, the condensers 2 a through 2 isequentially supply electrostatic energy to the condenser 11. Next, whenthe switch 7 is switched from the contact point T9 to the contact pointT10, the voltage V applied to the condenser 11 becomes equal to thepower supply voltage VH. In this way, the voltage V of the condenser 11rises from 0 to the power supply voltage VH in an approximatelystepped-up manner, as shown in FIG. 71(d).

[0283] Next, the switch 7 is switched from the contact point T10 to thecontact point T9. This connects the condenser 2 i of the accumulatingdevice 3 to the condenser 11.

[0284] Here, the electric charge accumulated in the condenser 2 i isC·V9, and the condenser 2 i substantially receives electric charge onlyfrom the condenser 11. The voltage V applied to the condenser 11 isaccordingly expressed as follows.

V=(CL·VH+C·V9)/(C+CL)

[0285] Further, the voltage V approximately equals to the voltage V9because the capacitance C of the condenser 2 i is sufficiently largerthan the capacitance CL of the condenser 11.

[0286] Here, the condenser 2 i supplies energy to the condenser 11during the step of connecting the condenser 11 to the condenser 2 iafter the condenser 11 is connected to the condenser 2 h, and theaccumulating device 3 does not receive energy from any circuit otherthan the condenser 11 between rising and falling edges of the voltagepulse. Thus, strictly speaking, the terminal voltage of the condenser 2i is not V9 but slightly smaller than V9 just before the condenser 11 isconnected to the condenser 2 i after connected to the power supplyterminal 9.

[0287] The terminal voltage of the condenser 2 i before the condenser 2i is connected to the condenser 11 is approximately V9. Strictlyspeaking, however, the condenser 2 i supplies energy to the condenser 11during the step of connecting the condenser 11 to the condenser 2 iafter the condenser 11 is connected to the condenser 2 h. As a result,the voltage of the condenser 2 i is slightly smaller than V9.

[0288] However, when the condenser 2 i having the terminal voltageslightly smaller than V9 is connected to the condenser 11 which ischarged to have the power supply voltage VH, the condenser 2 i collectselectrostatic energy (electric charge) from the condenser 11 and causesthe condenser 11 to discharge, because the terminal voltage of thecondenser 11, which is now the power supply voltage VH, is larger thanthe terminal voltage of the condenser 2 i. Here, the voltage of thecondenser 2 i is restored (regenerated) to a value approximately equalto V9 (value assumable to V9) by collecting energy from the condenser11.

[0289] After this, the switch 7 is switched from the contact point T9 tothe contact point T8, from the contact point T8 to the contact point T7,from the contact point T7 to the contact point T6, from the contactpoint T6 to the contact point T5, from the contact point T5 to thecontact point T4, from the contact point T4 to the contact point T3,from the contact point T3 to the contact point T2, and from the contactpoint T2 to the contact point T1. In accordance with this, thecondensers 2 a through 2 h sequentially collect energy from thecondenser 11. Finally, when the switch 7 is switched from the contactpoint T1 to the contact point T0, the condenser 11 is grounded so thatthe voltage V applied to the condenser 11 becomes 0, which is equal tothe ground.

[0290] In the manner described above, the voltage V of the condenser 11drops from the power supply voltage VH to 0 in an approximatelystepped-down manner, as shown in FIG. 71(d).

[0291] Note that, at the last step-down of the switch 7 (switching fromthe contact point T1 to the contact point T0), the electric chargeaccumulated in the condenser 11 is not sent back to the condensers 2 athrough 2 i and are all discarded to the ground. This means that part ofelectrostatic energy accumulated in the condenser 11 is discarded. Inthe present embodiment, the voltage V which is applied to the condenser11 is a maximum of VH, and the voltage V of the condenser 11 at the laststep-down of the switch 7 is V1, which equals to VH/10. In the presentembodiment, the condensers 2 a through 2 i collect most of the electriccharge which is discharged from the condenser 11 except the electriccharge at the last step-down of the switch 7, because the accumulatingdevice 3 does not receive energy from any circuit other than thecondenser 11 between the rising and falling edges of the voltage pulse.Hence, the electric charge accumulated in the condenser 11 is CL·VH, andthe electric charge discharged from the condenser 11 at the laststep-down of the switch 7 is CL·VH/10. Namely, the collection efficiencyof electrostatic energy is {fraction (9/10)}=90%.

[0292] In this way, the applied voltage V of the condenser 11 is steppedup by sequentially switching the switch 7 from the contact point T0through the contact point T10, and then stepped down by sequentiallyswitching the switch 7 from the contact point T10 through the contactpoint T0. With this, the condensers 2 a through 2 i of the accumulatingdevice 3 can supply electrostatic energy to the condenser 11, and cancollect most of the electrostatic energy thus accumulated in thecondenser 11.

[0293] As described above, the capacitive load drive circuit 1A of thepresent embodiment is so arranged that a voltage of the main powersource is divided into n and then accumulated in the accumulating device3; and the accumulating device 3 supplies electrostatic energy to thecondenser 11 and collects electrostatic energy that is discharged fromthe condenser 11 by switching the connection between the accumulatingdevice 3 and the condenser 11. This realizes highly efficient collectingand reusing of energy.

[0294] Further, the condensers 2 a through 2 i are switched in order ofsize of their terminal voltages. Because of this, an inrush currentsupplied to the condensers 2 a through 2 i and to the condenser 11 iskept low, thereby reducing energy loss. In addition, the condenser 11can be pulse-driven. Moreover, electrical power consumption can befurther reduced by arranging such that the switch 7 has a greater numbern of stages for switching over.

[0295] Further, the capacitive load drive circuits 1 and 1A ofEmbodiments 1 and 1A are arranged to have the voltage divider 5 composedof the resistors 4 which are connected in series. With this, theterminal voltages of the condensers 2 a through 2 i are adjusted to thepredetermined voltages V1 through V9. This realizes stable repeatingoperation.

[0296] Note that, in Embodiments 1 and 1A, differences between eachpossible voltage value for the output voltage V, namely V1-0, V2-V1,V3-V2, V4-V3, V5-V4, V6-V5, V7-V6, V8-V7, V9-V8, VH-V9, are set to bethe same value of VH/0, but the differences do not necessarily have thesame value. However, the differences having the same valueadvantageously achieve a high efficiency in energy collection. Moreover,when the differences have the same value, the inrush current supplied tothe condensers 2 a through 2 i and to the condenser 11 is kept furtherlower.

[0297] Further, in Embodiments 1 and 1A, the accumulating device 3 hasten condensers, but the number of condensers is not particularly limitedprovided that the accumulating device 3 has two or more condensers. Notethat, when the accumulating device 3 has n condensers (n is an integernot less than two), the efficiency in collecting electrostatic energy isn/(n+1).

[0298] Further, the capacitive load drive circuits 1 and 1A ofEmbodiments 1 and 1A use contact points T0 through T10 of the switch 7to generate a sequence of pulses. When a required pulse crest value islower than VH, however, driving operation can be sufficiently realizedby stopping the step-up of the voltage V of the condenser 11 at acertain voltage m·VH/10 (m is an integer not less than 2 and not morethan 9) without using all of the contact points of the switch 7. Forexample, when a required pulse crest value is 9VH/10, only the contactpoints T0 through T9 of the switch 7 may be used. Likewise, drivingoperation can be sufficiently carried out by stopping the step-up of thevoltage V of the condenser 11 at a certain voltage m·VH/10 (m is aninteger not less than 2 and not more than 9). When the step-up of thevoltage V of the condenser 11 is stopped at a certain voltage m·VH/10 (mis an integer not less than 2 and not more than 9), the efficiency incollecting electrostatic energy is (m-1)/ m.

[0299] In these methods that do not use all of the contact points of theswitch 7, the accumulating device 3 includes some condensers (among 2 athrough 2 i) whose energy supply to the condenser 11 and energycollection from the condenser 11 are imbalanced. Thus, it is necessaryto correct this imbalance caused by the energy supply from the voltagedivider 5 and the like.

[0300] Embodiment 1A is a method to reduce electrical power consumptionof a system in applying a voltage pulse to the condenser 11 which is acapacitive load. The method has the steps of sequentially supplyingenergy from the accumulating device 3 to the condenser 11 at a risingedge of the voltage waveform and conversely collecting energy from thecondenser 11 to the accumulating device 3 at a falling edge of thevoltage waveform. If the accumulating device 3 receives energy fromanother circuit between rising and falling edges of the voltage pulse,the efficiency of the accumulating device 3 in collecting energy fromthe condenser 11 decreases.

[0301] Accordingly, the imbalance generated in the accumulating device 3between the energy supply and the energy collection must be correctedwhen a waveform is not generated for the condenser 11, or must becorrected slowly over a longer time than a time for applying a waveformto the condenser 11.

[0302] Further, the rotary switch 7 is used in the capacitive load drivecircuits 1 and 1A of Embodiments 1 and 1A, but the switching means maybe eleven one-point contact switches provided in parallel, each havingone connection point; or a semiconductor switch.

[0303] [Embodiment 2]

[0304] The following will explain a further embodiment of the presentinvention with reference to FIGS. 4, 5(a) to 5(c), and 6(a) to 6(d).Note that, for convenience, members having the same functions as thoseused in Embodiment 1 will be given the same reference symbols, andexplanation thereof will be omitted here.

[0305] As shown in FIG. 4, a capacitive load drive circuit 20 of thepresent embodiment has the same arrangement as the capacitive load drivecircuit 1 of Embodiment 1 except that a switch (switching means) 17 isprovided instead of the switch 7 of Embodiment 1.

[0306] The switch 17 has the same arrangement as the rotary switch 7 ofEmbodiment 1 except that the contact point T0 is omitted.

[0307] Namely, when lowering (discharging) the voltage V of thecondenser 11, the switch 7 of Embodiment 1 is switched to the contactpoint T1 so as to cause the voltage V of the condenser 11 to be thevoltage V1, and then switched to the contact point T0 so as to lower thevoltage V of the condenser 11 to the potential equal to the ground (0).

[0308] In contrast, when lowering (discharging) the voltage V of thecondenser 11, the switch 17 of the present embodiment is switched to thecontact point T1 so as to cause the voltage V of the condenser 11 to bethe voltage V1, and then kept switched to the contact point T1 so as tokeep connecting the condenser 11 and the condenser 2 a having a smallestterminal voltage until the condenser 11 starts charging again.

[0309] Next, the operation of the capacitive load drive circuit 20 willbe explained with reference to FIGS. 5 and 6.

[0310] FIGS. 5(a) through 5(c) are timing charts showing the operationof the capacitive load drive circuit 20. FIG. 5(a) is a waveform chartshowing a waveform of the synchronizing signal SYNC which is supplied tothe switch 17. FIG. 5(b) is a waveform chart showing a waveform of thecontrol voltage Q of the transistor 6, which controls the operation ofthe transistor 6. FIG. 5(c) is a waveform chart showing a waveform ofthe voltage V which is applied to the condenser 11.

[0311] FIGS. 6(a) through 6(d), which show enlarged parts of the timingcharts shown in FIGS. 5(a) through 5(c), illustrate how the switch 17operates. FIG. 6(a) is an enlarged waveform chart showing a part of thewaveform of the synchronizing signal SYNC shown in FIG. 5(a). FIG. 6(b)is a timing chart showing how the switch 17 of FIG. 4 operates, namely,which one of the contact points T0 through T10 is connected. FIG. 6(c)is an enlarged waveform chart showing a part of the waveform of thecontrol voltage Q shown in FIG. 5(b). FIG. 6(d) is an enlarged waveformchart showing a part of the waveform of the voltage V shown in FIG.5(c).

[0312] As is understood from comparison between FIGS. 3(a) through (d)and FIGS. 6(a) through (d), the capacitive load drive circuit 20 of thepresent embodiment operates in the same manner as the capacitive loaddrive circuit 1 of Embodiment 1 except that the switch 17 is switched tothe contact T1 so as to cause the voltage V of the condenser 11 to beV1, during the period in which the switch 7 is switched to the contactpoint T0 in the capacitive load drive circuit 1 of Embodiment 1.

[0313] Specifically, in preparatory operation before starting thedriving operation of the condenser 11, the control voltage Q becomes ahigh level as shown in FIG. 5(b), so as to switch ON the transistor 6.With this, the predetermined voltages V1 through V9 are applied to thecondensers 2 a through 2 i of the accumulating device 3 as terminalvoltages, so as to charge the condensers 2 a through 2 i. Here, theswitch 17 is switched to the contact point T1. As a result, the voltageV of the condenser 11 rises to the voltage V1.

[0314] Next, the synchronizing signal SYNC is activated as shown in FIG.5(a), so as to start the driving operation. Then, by sequentiallyswitching the switch 17 from the contact point T1 through the contactpoint T9, the condensers 2 b through 2 i sequentially supplyelectrostatic energy to the condenser 11, so as to raise the voltage Vof the condenser 11 from the voltage V1 to the voltage V9. Next, whenthe switch 17 is switched form the contact point T9 to the contact pointT10, the condenser 11 is connected to the power supply terminal 9, sothat the voltage V applied to the condenser 11 equals to the powersupply voltage VH from the outside.

[0315] Next, the switch 17 is kept switched to the contact point T10 soas to hold the voltage V of the condenser 11 at the power supply voltageVH, then the switch 17 is sequentially switched from the contact pointT10 through the contact point T1. With this, the condensers 2 a through2 i sequentially collect energy from the condenser 11, so as to lowerthe voltage V of the condenser 11 from the voltage VH to the voltage V1.

[0316] Then, the voltage V1, which is not 0, keeps being applied to thecondenser 11 until the voltage V of the condenser 11 rises again, asdescribed above. Because of this, it is possible to retain theelectrostatic energy which is accumulated in the condenser 11, withoutdiscarding the electrostatic energy.

[0317] As described above, the output voltage V is stepped up bysequentially switching the switch 17; the output voltage V is thenstepped down to the voltage V1 which is not 0 by sequentially switchingthe switch 17 reversely; and this voltage is retained until the nextstep-up. With this arrangement, the electrostatic energy accumulated inthe condenser 11 can be retained and is not discarded. As a result, thecondensers 2 a through 2 i of the accumulating device 3 can collectalmost all of the electrostatic energy accumulated in the condenser 11,thereby further improving the efficiency in collecting electrostaticenergy.

[0318] In the capacitive load drive circuit 20 of the presentembodiment, the condenser 11 retains, as accumulated, electrostaticenergy corresponding to the voltage V1 at the last step-down, namelywhen the switch 17 is switched to the contact point T1. Thus, theelectrostatic energy accumulated in the condenser 11 can be supplied toother capacitive load or circuit, when the switch 17 is switched to thecontact point T1. Specifically, the electrostatic energy that thecondenser 2 a collects from the condenser 11 can be supplied to anexternal element other than the condenser 11 via an energy output path15 that is connected to the condenser 2 a having the smallest terminalvoltage, as shown in FIG. 4. This can reduce energy consumption of awhole apparatus including the capacitive load drive circuit 20 and theexternal element. This can also correct imbalance between energy supplyand energy collection in the condenser 2 a.

[0319] As a result, almost all of the electrostatic energy accumulatedin the condenser 11 can be reused. This can further improve efficiencyin reusing electrostatic energy. Note that, the external element otherthan the condenser 11 may be, for example, a memory circuit thatconsumes electrical power.

[0320] [Embodiment 2A]

[0321] The following will explain yet another embodiment of the presentinvention with reference to FIGS. 72, 73(a) to 73(c), and 74(a) to74(d). Note that, for convenience, members having the same functions asthose used in Embodiment 1, 1A, or 2 will be given the same referencesymbols, and explanation thereof will be omitted here.

[0322] A capacitive load drive circuit 20A of the present embodiment hasthe same arrangement as the capacitive load drive circuit 20 ofEmbodiment 2 except the following differences.

[0323] As a first difference, switches SW1 through SW9, which aresimilar to those in Embodiment 1A, are respectively provided between (i)nine connection points (voltage dividing points) a through i of thevoltage divider 5 and (ii) lines that respectively connect to thecontact points T1 through T9 in a capacitive load drive circuit 20A ofthe present embodiment, as shown in FIG. 72; whereas the nine connectionpoints (voltage dividing points) a through i of the voltage divider 5are directly connected to the lines that respectively connect to thecontact points T1 through T9 in the capacitive load drive circuit 20 ofEmbodiment 2.

[0324] As a second difference, the capacitive load drive circuit 20 ofEmbodiment 2 is provided with the transistor 6, and operates inaccordance with the timing charts shown in FIGS. 5 and 6, but thecapacitive load drive circuit 20A is provided with a switch 16A as inEmbodiment 1A, instead of the transistor 6, and operates in accordancewith timing charts shown in 73(a) to 73(c), or 74(a) to 74(d).

[0325] FIGS. 73(a) through 73(c) are timing charts showing the operationof the capacitive load drive circuit 20A. FIG. 73(a) is a waveform chartshowing a waveform of the synchronizing signal SYNC which is supplied tothe switch 7. FIG. 73(b) is a waveform chart showing a waveform of thecontrol voltage Q, which controls the operation of the switch 16A. FIG.73(c) is a waveform chart showing a waveform of the voltage V which isapplied to the condenser 11.

[0326] FIGS. 74(a) through 74(d) show another operation example of thecapacitive load drive circuit 20A. FIG. 74(a) is an enlarged waveformchart showing a part of the waveform of the synchronizing signal SYNCshown in FIG. 73(a). FIG. 74(b) is a timing chart showing how the switch7 of FIG. 1 operates, namely, which one of the contact points T0 throughT10 is connected. FIG. 74(c) is an enlarged waveform chart showing apart of the waveform of the control voltage Q which controls theoperation of the switch 16A. FIG. 74(d) is an enlarged waveform chartshowing a part of the waveform of the voltage V shown in FIG. 73(c).

[0327] Note that, the operation example of FIGS. 73(a) through 73(c)differs from the operation example of FIGS. 74 (a) through 74(d) in thesame manner that the operation example of FIGS. 70(a) through 70(c)differs from the operation example of FIGS. 71(a) through 71(d).

[0328] In the capacitive load drive circuit 20A of the presentembodiment, the condenser 11 retains, as accumulated, electrostaticenergy corresponding to the voltage V1 at the last step-down, namelywhen the switch 17 is switched to the contact point T1. Thus, theelectrostatic energy accumulated in the condenser 11 can be supplied toanother capacitive load or circuit, when the switch 17 is switched tothe contact point T1. Specifically, the electrostatic energy that thecondenser 2 a collects from the condenser 11 can be supplied to anexternal element other than the condenser 11 via an energy output path15 that is connected to the condenser 2 a having the smallest terminalvoltage, as shown in FIG. 72. This can reduce energy consumption of awhole apparatus including the capacitive load drive circuit 20 and theexternal element. This can also correct imbalance between energy supplyand energy collection in the condenser 2 a.

[0329] As a result, almost all of the electrostatic energy accumulatedin the condenser 11 can be reused. This can further improve efficiencyin reusing electrostatic energy. Note that, other than the condenser 11,the external element includes a memory circuit that consumes electricalpower, for example.

[0330] Further, energy is not supplied from another circuit to theaccumulating device 3 between rising and falling edges of the voltagepulse in the present embodiment, as a result of the foregoing first andsecond differences. This can prevent lowering of efficiency of theaccumulating device 3 in collecting energy from the condenser 11, thelowering caused by the energy supply from the other circuit.

[0331] [Embodiment 3]

[0332] The following will explain still another embodiment of thepresent invention with reference to FIG. 7. Note that, for convenience,members having the same functions as those used in Embodiment 1 will begiven the same reference symbols, and explanation thereof will beomitted here.

[0333] As shown in FIG. 7, a capacitive load drive circuit of thepresent embodiment is either the capacitive load drive circuit 1 ofEmbodiment 1 or the capacitive load drive circuit 1A of Embodiment 1Ashown in FIG. 75.

[0334] The present embodiment is the same as Embodiments 1 and 1A exceptfor an arrangement of the capacitive load driven by the capacitive loaddrive circuit 1 or 1A. In other words, the present embodiment differsform Embodiments 1 and 1A only in methods for using the capacitive loaddrive circuit 1 or 1A.

[0335] Namely, the capacitive load to be driven is the condenser 11 inEmbodiment 1 or 1A; whereas the capacitive load to be driven is aplurality of piezoids 21 provided in an ink-jet head 23, as shown inFIGS. 7 and 75. In addition to the piezoids 21, the ink-jet head 23 isprovided with analog switches 22 for connecting/disconnecting thecapacitive load drive circuit 1 or 1A and the piezoids 21.

[0336] According to this using method, the piezoids 21 having a highdielectric constant and a high capacitance are charged and discharged.With this, it is possible to collect and reuse energy highly efficientlywhen driving the ink-jet head 23 which is driven at a high repeatingfrequency and which consumes large electrical power.

[0337] The following will estimate electrical power consumption fordriving the ink-jet head 23 in (i) the capacitive load drive circuit 1Aof the present embodiment and (ii) the conventional capacitive loaddrive circuit which does not collect electrostatic energy.

[0338] First, it is assumed that the ink-jet head 23 has four heads ofYMCK, each of which is provided with sixty-four piezoids 21 and an inkjetting-out nozzle; and three color heads are simultaneously turned ONat most among the color heads. Here, the number of piezoids 21 connectedto the capacitive load drive circuit is up to 64×3. Accordingly, when acapacitance of each piezoid 21 is 80 pF, a sum of the capacitances ofthe piezoids 21 which are connected to the capacitive load drive circuitat the maximum is expressed as follows.

80×64×3=0.0153 μF

[0339] Then, when a rectangular wave having a crest value of 20 V and apulse width of 8 μs is applied to the piezoids 21 as a drive voltage inthe conventional load drive circuit, a current I that flows from thecapacitive load drive circuit to the piezoids 21 is expressed asfollows.

I=0.0153 μF×20V÷8 μs=0.0384A

[0340] Accordingly, electrical power consumption E per pulse in theconventional capacitive load drive circuit is expressed as follows.

E=0.0384A×20V=0.768W

[0341] On the other hand, when the ink-jet head 23 in the capacitiveload drive circuit 1A of the present embodiment operates in the samemanner as that in the conventional capacitive load drive circuit, andwhen V1=2(V), V2=4(V), V3=6(V), V4=8(V), V5=10(V), V6=12(V), V7=14(V),V8=16(V), V9=18(V), and VH=20(V), electrical power consumption per pulseis 0.077 W.

[0342] Therefore, the capacitive load drive circuit 1A of the presentembodiment consumes only a one-tenth amount of electrical power as theconventional capacitive load drive circuit. This one-tenth amount ofelectrical power is required for energy that is not sent back to thecondensers of the accumulating device 3 and is emitted to the ground atthe end. The remaining amount of energy is sent back to the condensersand is not consumed.

[0343] In the present example, a capacitance of each condenser 2 thatmakes up the accumulating device 3 needs to be larger than a loadcapacitance for driving the maximum number of piezoids 21 of the ink-jethead 23 (80×64×3=0.0153 μF in the above example) in order tosufficiently collect electrical power.

[0344] Note that, unlike a circuit which uses the LC resonance tocollect electrical power, the apparatus of the present embodiment usesthe condensers to collect electrical power. With this, it is possible tosimultaneously drive many capacitive loads (piezoids 21) with operatingcharacteristics (regeneration efficiency and the like) similar to thoseof the arrangement in which one capacitive load is driven.

[0345] [Embodiment 4]

[0346] The following will explain yet another embodiment of the presentinvention with reference to FIGS. 8, 9(a) to 9(c), 10(a) to 10(d), 11,and 12. Note that, for convenience, members having the same functions asthose used in Embodiment 1 will be given the same reference symbols, andexplanation thereof will be omitted here.

[0347] As shown in FIG. 8, a capacitive load drive circuit 30 of thepresent embodiment is the same as the capacitive load drive circuit 1 ofEmbodiment 1 except that a buffer circuit (buffer amplification means)31 is provided between the accumulating device 3 and the voltage divider5, and a transistor 16 is provided instead of the transistor 6.

[0348] Further, the capacitive load driven by the capacitive load drivecircuit 30 is the piezoids 21 which are provided in the ink-jet head 23as in Embodiment 3. In addition to the piezoids 21, the ink-jet head 23is provided with analog switches 22 as in Embodiment 3.

[0349] The voltage divider 5 divides a power supply voltage VH, which issupplied from the outside of the resistors 4, into voltages V1 throughV9 using ten resistors; and outputs the voltages V1 through V9 viaconnection points a through i between each resistor 4.

[0350] The buffer circuit 31 is composed of nine emitter followers 32,each of which is respectively inserted between (i) the connection pointsa through i between each resistor 4 of the voltage divider 5 and (ii)the condensers 2 a through 2 i.

[0351] The buffer circuit 31 adjusts the voltages V1 through V9 of thevoltage divider 5, and supplies the adjusted voltages V1′ through V9 tothe condensers 2 a through 2 i as terminal voltages. The emitterfollower 32 is an NPN emitter follower that uses an NPN transistor 32 ato raise the output voltages V1 through V9 to values higher than theinput voltages V1′ through V9′. With this, it is possible to prevent thecondensers 2 a through 2 i of the accumulating device 3 from having theterminal voltages lower than the predetermined voltages V1′ through V9′,in case where the electric charge in the condensers 2 a through 2 i ofthe accumulating device 3 becomes smaller than the initial electriccharge after collecting electric charge from the piezoids 21 which aredriven, where the voltages V1 through V9 and VH are positive voltages.Thus, it becomes possible to precisely adjust the terminal voltages ofthe condensers 2 a through 2 i of the accumulating device 3 to thepredetermined voltages V1′ through V9′.

[0352] Further, the buffer circuit 31 amplifies a current flowing in thevoltage divider 5 and outputs the amplified current to the condensers 2a through 2 i. This can reduce the amount of currents which flow throughthe resistors 4 of the voltage divider 5, so as to reduce electricalpower consumed at the voltage divider 5. As a result, it is possible tofurther reduce the electrical power consumption.

[0353] Further, the transistor 16 is a switch for switching ON/OFF thepower supply to the accumulating device 3 and the voltage divider 5. Thetransistor 16 is switched ON only during a predetermined period (periodfor supplying electrostatic energy), unlike the transistor 6 ofEmbodiments 1 through 3.

[0354] Next, the operation of the capacitive load drive circuit 30 willbe explained with reference to FIGS. 9(a) to 9(c), and FIGS. 10(a) to10(d).

[0355] FIGS. 9(a) through 9(c) are timing charts showing the operationof the capacitive load drive circuit 30. FIG. 9(a) is a waveform chartshowing a waveform of the synchronizing signal SYNC which is supplied tothe switch 17. FIG. 9(b) is a waveform chart showing a waveform of thecontrol voltage Q of the transistor 16, which controls the transistor16. FIG. 9(c) is a waveform chart showing a waveform of the voltage Vwhich is applied to the condenser 11.

[0356] FIGS. 10(a) through 10(d), which show enlarged parts of thetiming charts shown in FIGS. 9(a) through 9(c), illustrate how theswitch 7 operates. FIG. 10(a) is an enlarged waveform chart showing apart of the waveform of the synchronizing signal SYNC shown in FIG.9(a). FIG. 10(b) is a timing chart showing how the switch 7 of FIG. 8operates, namely, which one of the contact points T1 through T10 isconnected. FIG. 10(c) is an enlarged waveform chart showing a part ofthe waveform of the control voltage Q shown in FIG. 9(b). FIG. 10(d) isan enlarged waveform chart showing a part of the waveform of the voltageV shown in FIG. 9(c).

[0357] First, in preparatory operation before starting the drivingoperation of the condenser 11, the control voltage Q becomes a highlevel as shown in FIG. 9(b), so as to switch ON the transistor 16. Withthis, the output voltages V1′ through V9′ of the buffer circuit 31 areapplied to the condensers 2 a through 2 i of the accumulating device 3as terminal voltages. Then, after a predetermined period, the controlvoltage turns to a low level as shown in FIG. 9(b), so as to switch OFFthe transistor 16. The predetermined period is set enough to fullycharge the condensers 2 a through 2 i.

[0358] After the transistor 16 is switched OFF, the synchronizing signalSYNC is activated as shown in FIG. 9(a), so as to start the drivingoperation.

[0359] The driving operation is the same as that of Embodiment 1.Specifically, by sequentially switching the switch 7 from the contactpoint T0 through the contact point T9, the condensers 2 a through 2 isequentially supply electrostatic energy to the condenser 11, so as toraise the voltage V of the condenser 11 from 0 to the voltage V9′. Next,when the switch 7 is switched from the contact point T9 to the contactpoint T10, the condenser 11 is connected to the power supply terminal 9,so that the voltage V applied to the condenser 11 equals to the powersupply voltage VH from the outside.

[0360] Next, the switch 7 is kept switched to the contact point T10 soas to hold the voltage V of the condenser 11 at the power supply voltageVH over a longer period than the pulse width t of the synchronizingsignal SYNC, and then the switch 7 is sequentially switched from thecontact point T10 through the contact point T1. With this, thecondensers 2 a through 2 i sequentially collect energy from thecondenser 11, so as to lower the voltage V of the condenser 11 from thepower supply voltage VH to the voltage V1′.

[0361] Then, by switching the switch 7 from the contact point T1 to thecontact point T0, the condenser 11 is grounded so that the voltage Vapplied to the condenser 11 becomes 0, which is equal to the ground.

[0362] After this, the transistor 16 is switched ON for thepredetermined period until the condenser 11 starts a next drivingoperation.

[0363] In this way, the transistor 16 is switched ON for thepredetermined period when the drive voltage is not applied to thecondenser 11, namely when the condenser 11 is grounded. With this, thepower supply voltage VH is applied to the voltage divider 5 only duringthe predetermined period, thereby further reducing electrical powerconsumption.

[0364] Note that, the capacitive load drive circuit 30 of the presentembodiment is provided with the NPN emitter follower 32 that raises theoutput voltages V1′ through V9′ to values higher than the input voltagesV1 through V9 by using the NPN transistor 32 a, in order to deal withthe drop of the positive voltage.

[0365] When a negative voltage drops (absolute value of the negativevoltage decreases), however, it is preferable to replace the NPN emitterfollower 32 with a PNP emitter follower 33 that lowers the outputvoltage than the input voltage by using a PNP transistor 33 a, as shownin FIG. 11. With this, it is possible to prevent the condensers 2 athrough 2 i of the accumulating device 3 from having the terminalvoltages lower than the predetermined voltages V1′ through V9′, in casewhere the electric charge in the condensers 2 a through 2 i of theaccumulating device 3 becomes smaller than the initial electric chargeafter collecting electric charge from the piezoids 21 which are driven,where the voltages V1 through V9 and VH are negative voltages. Thus, itbecomes possible to precisely adjust the terminal voltages of thecondensers 2 a through 2 i of the accumulating device 3 to thepredetermined voltages V1′ through V9′.

[0366] Further, if a positive voltage V is outputted to the piezoids 21,the PNP emitter follower 33 as shown in FIG. 11 may be similarly usedinstead of the NPN emitter follower 32, in order to prevent the terminalvoltages of the condensers 2 a through 2 i of the accumulating device 3from being higher than the predetermined voltages V1′ through V9′, incase electric charge in the condensers 2 a through 2 i becomes largerthan the initial electric charge because of the piezoelectric effect dueto machine vibration, the influence of an inductive component of theload, and the like.

[0367] Further, if it is not predictable whether the terminal voltagesof the condensers 2 a through 2 i become higher or lower than thepredetermined voltages V1′ through V9′ when the circuit is operated, itis preferable to use an emitter follower of a totem-pole type 34 asshown in FIG. 12, instead of the NPN emitter follower 32. With thisarrangement in which a switch 16B is provided on the input side of eachchannel, it is possible to surely prevent the formation of an unexpectedstray-current path through which a base current flows to cause theincorrect operation of the circuit.

[0368] The capacitive load drive circuit 30 of the present embodiment isprovided with the emitter follower 32 as buffer amplification means(buffer means) having a voltage adjusting function, as described above.With this, it is possible to more precisely obtain the terminal voltages(V1′ through V9′) which are adjusted by the voltage divider 5, andreduce electrical power consumed by the voltage divider 5.

[0369] Further, in the capacitive load drive circuit 30 of the presentembodiment, the transistor 16 used as the switching section applies thepower supply voltage VH to the voltage divider 5 only during thepredetermined period, thereby further reducing electrical powerconsumption.

[0370] [Embodiment 4A]

[0371] The following will explain still another embodiment of thepresent invention with reference to FIGS. 76(a) and 76(b). Note that,for convenience, members having the same functions as those used inEmbodiment 1, 1A, or 3 will be given the same reference symbols, andexplanation thereof will be omitted here.

[0372] As shown in FIG. 76(a), a capacitive load drive circuit 30A isthe same as the capacitive load drive circuit 1A of Embodiment 1A,except that a buffer circuit (buffer amplification means) 31A isprovided between the accumulating device 3 and the voltage divider 5.

[0373] Further, the capacitive load driven by the capacitive load drivecircuit 30A is the piezoids 21 provided in the ink-jet head 23, as inEmbodiments 3 and 4. In addition to the piezoids 21, the ink-jet head 23is provided with the analog switches 22, as in Embodiments 3 and 4.

[0374] The voltage divider 5 divides a power supply voltage VH, which issupplied from the outside of the resistors 4, into voltages V1 throughV9 using ten resistors; and outputs the voltages V1 through V9 viaconnection points a through i between each resistor 4.

[0375] The buffer circuit 31A is composed of nine push-pulls 35, each ofwhich is respectively inserted between (i) the connection points athrough i between each resistor 4 of the voltage divider 5 and (ii) thecondensers 2 a through 2 i.

[0376] The buffer circuit 31A adjusts the voltages V1 through V9 of thevoltage divider 5, and supplies the adjusted voltages V1′ through V9 tothe condensers 2 a through 2 i as terminal voltages. The push-pull 35 isan emitter follower that uses an NPN transistor 35 a and a PNPtransistor 35 b to tune the output voltages V1 through V9 to the inputvoltages V1′ through V9′, as shown in FIG. 76(b). With this, it ispossible to prevent the condensers 2 a through 2 i of the accumulatingdevice 3 from having the terminal voltages lower than the predeterminedvoltages V1′ through V9′, in case where the electric charge in thecondensers 2 a through 2 i of the accumulating device 3 becomes smallerthan the initial electric charge after collecting electric charge fromthe piezoids 21 which are driven, where the voltages V1 through V9 andVH are positive voltages. Thus, it is possible to precisely adjust theterminal voltages of the condensers 2 a through 2 i of the accumulatingdevice 3 to the predetermined voltages V1′ through V9′. Conversely, itis also possible to prevent the condensers 2 a through 2 i of theaccumulating device 3 from having the terminal voltages higher than thepredetermined voltages V1′ through V9′, in case where the electriccharge in the condensers 2 a through 2 i of the accumulating device 3becomes larger than the initial electric charge after collectingelectric charge from the piezoids 21 which are driven. Thus, it ispossible to precisely adjust the terminal voltages of the condensers 2 athrough 2 i of the accumulating device 3 to the predetermined voltagesV1′ through V9′.

[0377] Further, the buffer circuit 31A amplifies a current flowing inthe voltage divider 5 and outputs the amplified current to thecondensers 2 a through 2 i. This can reduce the amount of currents whichflow through the resistors 4 of the voltage divider 5, so as to reduceelectrical power consumed by the voltage divider 5. As a result, it ispossible to further reduce the electrical power consumption.

[0378] The operation of the switch 16A is controlled by the controlvoltage Q whose waveform is shown in FIGS. 9(b) and 10(b).

[0379] The driving operation is the same as that of Embodiment 1A.Specifically, by sequentially switching the switch 7 from the contactpoint T0 through the contact point T9, the condensers 2 a through 2 isequentially supply electrostatic energy to the piezoids 21, so as toraise the voltage V of the piezoids 21 from 0 to the voltage V9′. Next,when the switch 7 is switched from the contact point T9 to the contactpoint T10, the piezoids 21 are connected to the power supply terminal 9,so that the voltage V applied to the piezoids 21 equals to the powersupply voltage VH from the outside.

[0380] Next, the switch 7 is kept switched to the contact point T10 soas to hold the voltage V of the piezoids 21 at the power supply voltageVH over a longer period than the pulse width t of the synchronizingsignal SYNC, and then the switch 7 is sequentially switched from thecontact point T10 through the contact point T1. With this, thecondensers 2 a through 2 i sequentially collect energy from the piezoids21, so as to lower the voltage V of the piezoids 21 from the powersupply voltage VH to the voltage V1′.

[0381] Then, by switching the switch 7 from the contact point T1 to thecontact point T0, the piezoids 21 are grounded so that the voltage Vapplied to the piezoids 21 becomes 0, which is equal to the ground.

[0382] The capacitive load drive circuit 30A of the present embodimentis provided with the push-pulls 35 as buffer amplification means (buffermeans) having a voltage adjusting function, as described above. Withthis, it is possible to more precisely obtain the terminal voltages (V1′through V9′) which are adjusted by the voltage divider 5, and reduceelectrical power consumed by the voltage divider 5.

[0383] [Embodiment 5]

[0384] Next, the following will explain yet another embodiment of thepresent invention with reference to FIGS. 13 and 14(a) to 14(c). Notethat, for convenience, members having the same functions as those usedin Embodiment 1 will be given the same reference symbols, andexplanation thereof will be omitted here.

[0385] As shown in FIG. 13, a capacitive load drive circuit 40 of thepresent embodiment is provided with the accumulating device 3 composedof the condensers 2 a through 2 i, and the voltage divider 5 composed ofthe resistors 4 each having a resistance of 1 kΩ, for example, like thecapacitive load drive circuit 1 of Embodiment 1.

[0386] The capacitive load drive circuit 40 of the present embodimentapplies voltages VA, VB, and VC having different phases from oneanother, respectively to condensers 11A, 11B, and 11C which arecapacitive loads, so as to charge and discharge the condensers 11A, 11B,and 11. In other words, the capacitive load to be driven is divided intothree phases: namely, the condenser 11A to which the voltage VA in Aphase is applied, the condenser 11B to which the voltage VB in B phaseis applied, and the condenser 11C to which the voltage VC in C phase isapplied.

[0387] In the present embodiment, unlike previous Embodiments, outputlines 37, 38, and 39 through which the accumulating device 3 and thevoltage divider 5 output the voltages VA, VB, and VC to the condensers11A, 11B, and 11C, respectively, are separated into two different kindsof paths. Namely, the output lines 37, 38, and 39 are separated into (i)charge paths (energy supplying path) 37 a, 38 a, and 39 a through whichthe accumulating device 3 supplies electrostatic energy to thecondensers 11A, 11B, and 11C, and (ii) discharge paths (energycollecting path) 37 b, 38 b, and 39 b through which the accumulatingdevice 3 collects electrostatic energy from the condensers 11A, 11B, and11C.

[0388] The charge paths 37 a, 38 a, and 39 a are provided withrectifying diodes (rectifying means) 65 that regulate a current to flowin a direction from the accumulating device 3 toward the condensers 11A,11B, and 11C; whereas the discharge paths 37 b, 38 b, and 39 b areprovided with rectifying diodes (rectifying means) 66 that regulate acurrent to flow in a direction from the condensers 11A, 11B, and 11Ctoward the accumulating device 3. With this, a voltage from theaccumulating device 3 is applied to the capacitive load via the chargepaths 37 a, 38 a, and 39 a, and electrostatic energy discharged from thecondensers 11A, 11B, and 11C are sent back to the accumulating device 3via the discharge paths 37 b, 38 b, and 39 b.

[0389] Further, instead of the rotary switch 7 in Embodiment 1, thecapacitive load drive circuit 40 of the present embodiment is providedwith (A) transistors 67A, 67B, 67C, 68A, 68B, and 68C, (B) switchingcircuits (switching means) 50 composed of nine transistors 41 through 49and switching circuits (switching means) 60 composed of nine transistors51 through 59, (C) a selecting circuit (selecting means) 62 composed oftransistors 61A, 61B, and 61C, and (D) a selecting circuit (selectingmeans) 64 composed of transistors 63A, 63B, and 63C.

[0390] The transistors 67A, 67B, and 67C correspond to the contact pointT10 of the switch 7 in Embodiment 1. The transistors 67A, 67B, and 67Csupply the power supply voltage VH which is sent from the power supplyterminal 9 to the condensers 11A, 11B, and 11C via the output lines 37,38, and 39; and are switched ON only during a period corresponding tothe period when the switch 7 is switched to the contact point T10 inEmbodiment 1. Note that, the transistors 67A, 67B, and 67C are providedwith diodes 69 for protecting the transistors 67A, 67B, and 67C.

[0391] The transistors 68A, 68B, and 68C correspond to the contact pointT0 of the switch 7 in Embodiment 1. The transistors 68A, 68B, and 68Cground the condensers 11A, 11B, and 11C via the output lines 37, 38, and39; and are switched ON only during a period corresponding to the periodwhen the switch 7 is switched to the contact point T0 in Embodiment 1.Note that, the transistors 68A, 68B, and 68C are provided with diodes 73for protecting the transistors 68A, 68B, and 68C.

[0392] The nine transistors 41, 42, 43, 44, 45, 46, 47, 48, and 49 ofthe switching circuit 50 and the nine transistors 51, 52, 53, 54, 55,56, 57, 58, and 59 of the switching circuit 60 respectively correspondto the contact points T1, T2, T3, T4, T5, T6, T7, T8, and T9 of theswitch 7 in Embodiment 1.

[0393] The switching circuit 50 is provided at the charge paths 37 a, 38a, and 39 a. The transistors 41, 42, 43, 44, 45, 46, 47, 48, and 49respectively have one ends respectively connected to the condensers 2 a,2 b, 2 c, 2 d, 2 e, 2 f, 2 g, 2 h, and 2 i via the voltage divider 5,and the other ends commonly connected to the transistors 61A, 61B, and61C to be described later. The transistors 41, 42, 43, 44, 45, 46, 47,48, and 49 are switched ON only during periods corresponding to theperiods where the switch 7 is switched to the contact points T1, T2, T3,T4, T5, T6, T7, T8, and T9, respectively, during the period (chargeperiod) in which the voltage is stepped up in Embodiment 1.

[0394] The switching circuit 60 is provided at the discharge paths 37 b,38 b, and 39 b. The transistors 51, 52, 53, 54, 55, 56, 57, 58, and 59have one ends respectively connected to the condensers 2 a, 2 b, 2 c, 2d, 2 e, 2 f, 2 g, 2 h, and 2 i via the voltage divider 5, and the otherends commonly connected to the transistors 63A, 63B, and 63C to bedescribed later. The transistors 51, 52, 53, 54, 55, 56, 57, 58, and 59are switched ON only during periods corresponding to the periods wherethe switch 7 is switched to the contact points T1, T2, T3, T4, T5, T6,T7, T8, and T9, respectively, during the period (discharge period) inwhich the voltage is stepped down in Embodiment 1.

[0395] Thus, only one of the transistor 68A (or 68B or 68C), thetransistor 67A (or 67B or 67C), the transistors 41, 42, 43, 44, 45, 46,47, 48, and 49, and the transistors 51, 52, 53, 54, 55, 56, 57, 58, and59 is selectively switched ON. Further, the transistors 68A (or 68B or68C), 41, 42, 43, 44, 45, 46, 47, 48, 49, 67A (or 67B or 67C), 59, 58,57, 56, 55, 54, 53, 52, 51, and 68A (or 68B or 68C) are sequentiallyselected in this order. Accordingly, pulse voltages stepping up and downin an approximately trapezoidal shape as shown in FIGS. 14(a) through14(c) are applied to the condensers 11A, 11B, and 11C as the voltagesVA, VB, VC, as in Embodiment 1. Further, the condensers 2 a, 2 b, 2 c, 2d, 2 e, 2 f, 2 g, 2 h, and 2 i supply electrostatic energy to thecondensers 11A, 11B, and 11C when the voltages VA, VB, and VC rise, andthe condensers 2 a, 2 b, 2 c, 2 d, 2 e, 2 f, 2 g, 2 h, and 2 i collectelectrostatic energy from the condensers 11A, 11B, and 11C when thevoltages VA, VB, and VC fall, as in Embodiment 1.

[0396] The selecting circuit 62 is provided at the charge paths 37 a, 38a, and 39 a, and switches ON/OFF the transistors 61A, 61B, and 61Cprovided inside, so as to selectively charge one of the condensers 11Athrough 11C. By using, as switches, the transistors 61A, 61B, and 61Cprovided at the charge paths 37 a, 38 a, and 39 a, an output voltage ofthe switching circuit 50 can be selectively applied to one of thecondensers 11A through 11C, thereby charging the condensers 11A through11C at different timings.

[0397] The selecting circuit 64 is provided at the discharge paths 37 b,38 b, and 39 b, and switches ON/OFF the transistors 63A, 63B, and 63Cprovided inside, so as to selectively charge one of the condensers 11Athrough 11C. By using, as switches, the transistors 63A, 63B, and 63Cprovided at the discharge paths 37 b, 38 b, and 39 b, an output voltageof the switching circuit 60 can be selectively applied to one of thecondensers 11A through 11C, thereby charging the condensers 11A through11C at different timings.

[0398] An example of such an operation is shown in timing charts ofFIGS. 14(a), 14(b), and 14(c). FIGS. 14(a), 14(b), and 14(c)respectively show how the voltages VA, VB, and VC, which are applied tothe condensers 11A, 11B, and 11C, respectively, change as time elapses.The transistors 61A, 61B, and 61C provided at the charge paths 37 a, 38a, and 39 a, and the transistors 63A, 63B, and 63C provided at thedischarge paths 37 b, 38 b, and 39 b are used as switches to adjust theON/OFF timings, so as to drive the condensers 11A through 11C at thetimings shown in FIGS. 14(a) through 14(c).

[0399] As described above, in the capacitive load drive circuit 40 ofthe present embodiment, the condensers 2 a, 2 b, 2 c, 2 d, 2 e, 2 f, 2g, 2 h, and 2 i can collect and reuse most of the electrostatic energywhich are accumulated in the condensers 11A, 11B, and 11C, as inEmbodiment 1.

[0400] Further, the capacitive load drive circuit 40 of the presentembodiment is provided with the selecting circuits 62 and 64 forselecting the plurality of condensers 11A through 11C, so as to applyvoltages to the plurality of condensers 11A through 11C at differenttimings.

[0401] Further, the capacitive load drive circuit 40 of the presentembodiment is so arranged that the charge paths 37 a, 38 a, and 39 a andthe discharge paths 37 b, 38 b, and 39 b are separated from each other.

[0402] With this, it is possible to control the timing for charging andthe timing for discharging independently, so as to allow one condenser11B to be charged during a discharge period of the other condenser 11A,as shown in FIGS. 14(a) through 14(c). Further, by separating the chargepaths 37 a, 38 a, and 39 aand the discharge paths 37 b, 38 b, and 39 bfrom each other, it is possible to optimize the charge characteristicand the discharge characteristic independently.

[0403] [Embodiment 5A]

[0404] The following will explain still another embodiment of thepresent invention with reference to FIG. 77. Note that, for convenience,members having the same functions as those used in Embodiment 1, 1A, or5 will be given the same reference symbols, and explanation thereof willbe omitted here.

[0405] A capacitive load drive circuit 40A of the present embodiment hasthe same arrangement as the capacitive load drive circuit 40 ofEmbodiment 2 except the following differences.

[0406] As a first difference, switches SW1 through SW9 as in Embodiment1A are respectively provided between (i) nine connection points (voltagedividing points) a through i of the voltage divider 5 and (ii) linesthat respectively connect to the contact points T1 through T9 in acapacitive load drive circuit 40A of the present embodiment, as shown inFIG. 77; whereas the nine connection points (voltage dividing points) athrough i of the voltage divider 5 are directly connected to the linesthat respectively connect to the contact points T1 through T9 in thecapacitive load drive circuit 40 of Embodiment 5.

[0407] As a second difference, the capacitive load drive circuit 40A isprovided with the switch 16A as in Embodiment 1A.

[0408] In the present embodiment, energy is not supplied from anothercircuit to the accumulating device 3 between rising and falling edges ofthe voltage pulse in the present embodiment, as a result of theforegoing first and second differences. This can prevent lowering ofefficiency of the accumulating device 3 in collecting energy from thecondenser 11, the lowering caused by the energy supply from the othercircuit.

[0409] [Embodiment 6]

[0410] The following will explain yet another embodiment of the presentinvention with reference to FIGS. 15 and 16(a) to 16(c). Note that, forconvenience, members having the same functions as those used inEmbodiment 1 or 5 will be given the same reference symbols, andexplanation thereof will be omitted here.

[0411] A capacitive load drive circuit 70 of the present embodiment isthe same as the capacitive load drive circuit 40 of Embodiment 5 exceptthat rectifying diodes (rectifying means) 71 and 72 are respectivelyprovided to the switching circuits 50 and 60 between the switchingcircuits 50 and 60 and the selecting circuits 62 and 64.

[0412] The rectifying diodes 71 are respectively provided to thetransistors 41 through 49 of the switching circuit 50 on the side of theselecting circuit 62. The rectifying diodes 72 are respectively providedto the transistors 51 through 59 of the switching circuit 60 on the sideof the selecting circuit 64.

[0413] By providing the rectifying diodes 71 and 72 as described above,a short-circuit current does not flow even when the delay in the ON/OFFoperation of the switching circuits 50 and 60 and the like causes aplurality of transistors (41 through 49, and 51 through 59) to beswitched ON in the switching circuit 50 or the switching circuit 60,thereby preventing the breakage of the circuit.

[0414] In the present embodiment, the capacitive load to be driven isdivided into three phases: namely, the condenser 11A to which thevoltage VA in A phase is applied, the condenser 11B to which the voltageVB in B phase is applied, and the condenser 11C to which the voltage VCin C phase is applied, as in Embodiment 5.

[0415] Further, in the present embodiment, as in Embodiment 5, by using,as switches, the transistors 61A, 61B, and 61C provided at the chargepaths 37 a, 38 a, and 39 aand the transistors 63A, 63B, and 63C providedat the discharge paths 37 b, 38 b, and 39 b, an output voltage of theswitching circuit 60 can be selectively applied to one of the condensers11A through 11C, thereby charging the condensers 11A through 11C atdifferent timings.

[0416] An example of such an operation is shown in timing charts ofFIGS. 16(a), 16(b), and 16(c). FIGS. 16(a), 16(b), and 16(c)respectively show how the voltages VA, VB, and VC, which are applied tothe condensers 11A, 11B, and 11C, respectively, change as time elapses.The transistors 61A, 61B, and 61C provided at the charge paths 37 a, 38a, and 39 a, and the transistors 63A, 63B, and 63C provided at thedischarge paths 37 b, 38 b, and 39 b are used as switches to adjust theON/OFF timings, so as to drive the condensers 11A through 11C at thetimings shown in FIGS. 16(a) through 16(c).

[0417] [Embodiment 6A]

[0418] The following will explain still another embodiment of thepresent invention with reference to FIG. 78. Note that, for convenience,members having the same functions as those used in Embodiment 1, 1A, or6 will be given the same reference symbols, and explanation thereof willbe omitted here.

[0419] A capacitive load drive circuit 70A of the present embodiment hasthe same arrangement as the capacitive load drive circuit 70 ofEmbodiment 2 except the following differences.

[0420] As a first difference, switches SW1 through SW9 as in Embodiment1A are respectively provided between (i) nine connection points (voltagedividing points) a through i of the voltage divider 5 and (ii) linesthat respectively connect to the contact points T1 through T9 in acapacitive load drive circuit 70A of the present embodiment, as shown inFIG. 78; whereas the nine connection points (voltage dividing points) athrough i of the voltage divider 5 are directly connected to the linesthat respectively connect to the contact points T1 through T9 in thecapacitive load drive circuit 70 of Embodiment 6.

[0421] As a second difference, the capacitive load drive circuit 70A isprovided with the switch 16A as in Embodiment 1A.

[0422] In the present embodiment, energy is not supplied from anothercircuit to the accumulating device 3 between rising and falling edges ofthe voltage pulse in the present embodiment, as a result of theforegoing first and second differences. This can prevent lowering ofefficiency of the accumulating device 3 in collecting energy from thecondenser 11, the lowering caused by the energy supply from the othercircuit.

[0423] [Embodiment 7]

[0424] The following will explain yet another embodiment of the presentinvention with reference to FIGS. 17, 18(a), 18(b), and 19. Note that,for convenience, members having the same functions as those used inEmbodiment 1 will be given the same reference symbols, and explanationthereof will be omitted here.

[0425] A capacitive load drive circuit 81 of the present embodimentdiffers from the capacitive load drive circuit 1 of Embodiment 1 inthat, as shown in FIG. 17, the capacitive load drive circuit 81 of thepresent embodiment is provided with a voltage divider 85 which dividesand sets a voltage using zener diodes 84A through 84E as constantvoltage means (constant voltage elements) for stabilizing the dividedvoltages; whereas the capacitive load drive circuit of Embodiment 1 isprovided with the voltage divider 5 which divides and sets a voltageusing the resistors 4.

[0426] Further, the capacitive load drive circuit 81 of the presentembodiment differs from the capacitive load drive circuit 1 ofEmbodiment 1 in that an accumulating device 83 in which condensers(energy accumulating elements) 82A through 82E are connected in seriesis provided instead of the accumulating device 3 in which the condensers2 a through 2 i are connected in parallel.

[0427] Further, the capacitive load drive circuit 81 of the presentembodiment differs from the capacitive load drive circuit 1 ofEmbodiment 1 in that a switching circuit (switching means) 87 composedof a plurality of switches 91 through 96 is provided instead of therotary switch 7.

[0428] The voltage divider 85 divides the power supply voltage VH intopredetermined voltages V1 through V4 using the zener diodes 84A, 84B,84C, 84D, and 84E which are a plurality of constant voltage elementsconnected in series between the power supply terminal 9 and the ground.Then, the voltage divider 85 outputs the predetermined voltages V1through V4 to the accumulating device 83 from connection points betweenthe zener diodes 84A, 84B, 84C, 84D, and 84E.

[0429] The accumulating device 83 is so arranged that the condensers82A, 82B, 82C, 82D, and 82E are sequentially connected in series in thisorder from the ground to the power supply terminal 9. The condenser 82Ahas one end grounded and the other end to which the voltage V1 isapplied from the voltage divider 85. Further, the voltage V1 and thevoltage V2 are respectively applied to ends of the condenser 82B, thevoltage V2 and the voltage V3 are respectively applied to ends of thecondenser 82C, and the voltage V3 and the voltage V4 are respectivelyapplied to ends of the condenser 82D. Further, the condenser 82E has oneend to which the power supply voltage VH is supplied from the powersupply terminal 9, and the other end to which the voltage V4 is appliedfrom the voltage divider 85.

[0430] The six switches 91 through 96 of the switching circuit 87basically correspond to the contact points T0 through T10 of the switch7. In other words, the switching circuit 87 selectively switches ON oneof the switches 91 through 96. The switch 91 is grounded, the voltagesV1, V2, V3, and V4 supplied from the accumulating device 83 and thevoltage divider 85 are respectively applied to the switches 92 through95, and the switch 96 is connected to the power supply terminal 9. In aninitial state, the switch 91 is selected. Then, by sequentiallyselecting the switches 92, 9S(4), and 95 in this order, electrostaticenergy is sequentially supplied from the condensers 82A through 82E tothe condenser 11, so as to raise the voltage V of the condenser 11 from0 to the voltage V4. Next, by selecting the switch 96, the condenser 11is connected to the power supply terminal 9, so that the voltage Vapplied to the condenser 11 becomes equal to the power supply voltage VHfrom the outside.

[0431] Next, the switch 96 is kept switched ON for a predeterminedperiod so as to hold the voltage of the condenser 11 at the power supplyvoltage VH. Then, by sequentially selecting the switches 95, 94, 9S(2)in this order, energy is sequentially collected from the condenser 11 tothe condensers 82A through 82E, so as to lower the voltage V of thecondenser 11 from the power supply voltage VH to the voltage V1.

[0432] After this, by selecting the switch 91, the condenser 11 isgrounded so that the voltage V applied to the condenser 11 becomes 0,which is equal to the ground.

[0433] Next, the operation principle of the voltage divider 85 will beexplained with reference to FIGS. 18(a) and 18(b).

[0434] As shown in FIG. 18(a), when a current from the condenser 11flows into the terminal voltage V2 of the zener diode 84B on the cathodeside in such a direction as to raise an output terminal voltage(potential of the switch 93) P2, a load current flows into thecondensers 82A and 82B in response to the current flowing in and out ofthe condenser 11, so as to absorb the current from the condenser 11.Concurrently, the zener diodes 84A and 84B have deeper operating pointso that their impedances are lowered. Thus, a current flows from thecondenser 11 to the ground line via the zener diodes 84A and 84B so thatthe output terminal voltage P2 maintains the zener voltage V2.

[0435] Further, as shown in FIG. 18(b), when a current from thecondenser 11 flows in and out of the terminal voltage V2 of the zenerdiode 84C on the anode side in such a direction as to lower the outputterminal voltage P2, a current flows from the condensers 82C, 82D, and82E to the condenser 11 in response to the current flowing in and out ofthe condenser 11, so as to absorb the current flowing in and out of thecondenser 11. Concurrently, the zener diodes 84C, 84D and 84E havedeeper operating point so that their impedances are lowered. Thus, acurrent flows from the power supply line to the condenser 11 via thezener diodes 84C, 84D, and 84E so that the output terminal voltage P2maintains the zener voltage V2.

[0436] As described above, the zener diodes 84A, 84B, 84C, 84D, and 84Eabsorb the current flowing in and out of the condenser 11 which raisesor lowers the output terminal voltage P2. Strictly speaking, the zenervoltages of the zener diodes 84A, 84B, 84C, 84D, and 84E change as theoperating point varies. However, the changes are so slight as to bepractically negligible. Therefore, the output terminal voltages P1through P4, namely the terminal voltages 82A through 82E, can bemaintained to be constant.

[0437] Note that, the capacitive load drive circuit 81 of the presentembodiment may be provided with a buffer circuit 102 in which condensers101A, 101B, 101C, 101D, and 101E are sequentially connected in series inthis order from the ground to the power supply terminal 9, as in acapacitive load drive circuit 100 shown in FIG. 19. With this, it ispossible to buffer and absorb a current flowing from the condenser 11into the voltage divider 85, or a current flowing out of the voltagedivider 85 to the condenser 11. This can reduce the workload of thezener diodes 84A, 84B, 84C, 84D, and 84E.

[0438] Further, as in the capacitive load drive circuit 100 shown inFIG. 19, current-limit resistors 103, 104, 105, and 106 may berespectively inserted between (i) connection points between the zenerdiodes 84A, 84B, 84C, 84D, and 84E and (ii) connection points betweenthe condensers 82A, 82B, 82C, 82D, and 82E, so as to form acounter-change adjusting section 107. This can further reduce theworkload of the zener diodes 84A, 84B, 84C, 84D, and 84E.

[0439] [Embodiment 7A]

[0440] The following will explain still another embodiment of thepresent invention with reference to FIGS. 79 and 80. Note that, forconvenience, members having the same functions as those used inEmbodiment 1 or 7 will be given the same reference symbols, andexplanation thereof will be omitted here.

[0441] A capacitive load drive circuit 81A of the present embodiment hasthe same arrangement as the capacitive load drive circuit 81 ofEmbodiment 2 except the following difference.

[0442] As the difference, switches SW12 through SW16 similar to theswitches SW1 through SW9 of Embodiment 1A are respectively providedbetween (i) five connection points other than the grounded connectionpoint among the six connection points of the voltage divider 5 and (ii)the switches 92 through 96 in the capacitive load drive circuit 70A ofthe present embodiment, as shown in FIGS. 79 and 80; whereas the sixconnection points of the voltage divider 5 are directly connected to theswitches 91 through 96 in the capacitive load drive circuit 70 ofEmbodiment 6.

[0443] In the present embodiment, energy is not supplied from anothercircuit to the accumulating device 3 between rising and falling edges ofthe voltage pulse in the present embodiment, as a result of theforegoing first and second differences. This can prevent lowering ofefficiency of the accumulating device 3 in collecting energy from thecondenser 11, the lowering caused by the energy supply from the othercircuit.

[0444] [Embodiment 8]

[0445] The following will explain yet another embodiment of the presentinvention with reference to FIG. 20. Note that, for convenience, membershaving the same functions as those used in Embodiment 1 or 8 will begiven the same reference symbols, and explanation thereof will beomitted here.

[0446] In the arrangement of Embodiment 7, the zener diodes 84A, 84B,84C, 84D, and 84E may burn out when the power supply voltage VH becomeslarger than a sum of zener voltages of the zener diodes 84A, 84B, 84C,84D, and 84E due to (i) unevenness in the power supply voltage and ineach of zener voltages of the zener diodes 84A, 84B, 84C, 84D, and 84E;(ii) changes over time; and (iii) temperature changes. Further, in thearrangement of Embodiment 7, each terminal voltage of the zener diodes82A, 82B, 82C, 82D, and 82E may become uncertain when the power supplyvoltage VH becomes smaller than a sum of zener voltages of the zenerdiodes 84A, 84B, 84C, 84D, and 84E.

[0447] The present embodiment will explain a capacitive load drivecircuit that solves the above problems.

[0448] As shown in FIG. 20, a capacitive load drive circuit 110 of thepresent embodiment is so arranged that a pull-up resistor 108 is usedinstead of the zener diode 84E, and a terminal of the zener diode 84D ispulled up to a power supply line 97 by using the pull-up resistor 108 inthe capacitive load drive circuit 81 of Embodiment 7. Namely, thecapacitive load drive circuit 110 is so arranged that the stage that isclosest to the power supply line 97 (uppermost stage) absorbs adifference between (i) the sum of zener voltages of the zener diodes84A, 84B, 84C, 84D, and 84E and (ii) the power supply voltage VH. Withthis arrangement, the power supply line 97 supplies a bias current tothe zener diodes 84A, 84B, 84C, and 84D via the pull-up resistor 108,thereby stabilizing the terminal voltages of the condensers 82A, 82B,82C, 82D, and 82E. Here, the sum of zener voltages of the zener diodes84A, 84B, 84C, 84D, and 84E is set lower than the power supply voltageVH.

[0449] Further, as in the capacitive load drive circuit 100 shown inFIG. 19, current-limit resistors 103, 104, 105, and 106 may berespectively inserted between (i) connection points between the zenerdiodes 84A, 84B, 84C, and 84D and the pull-up resistor 108 and (ii)connection points between the condensers 82A, 82B, 82C, 82D, and 82E soas to form a counter-change adjusting section 107 in the capacitive loaddrive circuit 110 of the present embodiment. This can further reduce theworkload of the zener diodes 84A, 84B, 84C, and 84D.

[0450] Note that, apart from the arrangement in which the pull-upresistor 108 is provided, a pull-down resistor may be used instead ofthe zener diode 84A in the capacitive load drive circuit 81 ofEmbodiment 7, so as to pull down a terminal of the zener diode 84D to aground line 98 by using the pull-down resistor. With this, the sameeffects can be achieved as in the arrangement employing the pulling-up,thereby stabilizing the terminal voltages of the condensers 82A, 82B,82C, 82D, and 82E.

[0451] [Embodiment 9]

[0452] The following will explain still another embodiment of thepresent invention with reference to FIG. 21. Note that, for convenience,members having the same functions as those used in Embodiment 1 or 7will be given the same reference symbols, and explanation thereof willbe omitted here.

[0453] The present embodiment will explain a capacitive load drivecircuit that solves the problems regarding the difference between (i)the sum of zener voltages of the zener diodes 84A, 84B, 84C, 84D, and84E and (ii) the power supply voltage VH as described in Embodiment 8.

[0454] In order to arrange such that the intermediate stages absorb thedifference between the power supply voltage VH and the sum of zenervoltages of the zener diodes 84A, 84B, 84C, and 84D, a capacitive loaddrive circuit 120 of the present embodiment is so arranged that thezener diodes (84A, 84B, 84C, 84D, and 84E) are separated into those onthe power supply line 97 side (84D and 84E) and those on the ground line98 side (84A and 84B). Further, the zener diodes 84D and 84E on thepower supply line 97 side are pulled up to the power supply line 97 byusing a pull-up resistor 111, and the zener diodes 84A and 84B on theground line 98 side are pulled down to the ground line 98 by using apull-down resistor 112, so as to supply a bias current to the zenerdiodes 84A, 84B, 84D, and 84E. Here, the sum of zener voltages of thezener diodes 84A, 84B, 84C, 84D, and 84E is set lower than the powersupply voltage VH.

[0455] The capacitive load drive circuit 120 is provided with a voltagedivider 113 composed of a first voltage divider 113A and a secondvoltage divider 113B which are connected in parallel between the powersupply line 97 and the ground line 98. The first voltage divider 113Aincludes the zener diodes 84A and 84B which are connected in seriesbetween the power supply line 97 and the ground line 98, and the pull-upresistor 111 is inserted between (i) the zener diodes 84A and 84B and(ii) the power supply line 97. The second voltage divider 113B includesthe zener diodes 84D and 84E which are connected in series between thepower supply line 97 and the ground line 98, and the pull-down resistor112 is inserted between (i) the zener diodes 84D and 84E and (ii) theground line 98.

[0456] In this way, by absorbing the difference between the power supplyvoltage VH and the sum of zener voltages of the zener diodes 84A, 84B,84C, and 84D at the intermediate stages, it is possible to maintain thestability of terminal voltages in the vicinity of the power supply line97 and in the vicinity of the ground line 98.

[0457] Further, as in the capacitive load drive circuit 100 shown inFIG. 19, current-limit resistors 103, 104, 105, and 106 are respectivelyinserted between (i) connection points between the zener diodes 84A,84B, 84C, and 84D, the pull-up resistor 111, and the pull-down resistor112 and (ii) connection points of the condensers 82A, 82B, 82C, 82D, and82E so as to form a counter-change adjusting section 107 in thecapacitive load drive circuit 120 of the present embodiment. This canfurther reduce the workload of the zener diodes 84A, 84B, 84C, and 84D,and 84E.

[0458] [Embodiment 10]

[0459] The following will explain yet another embodiment of the presentinvention with reference to FIG. 22. Note that, for convenience, membershaving the same functions as those used in Embodiment 1, 7, or 9 will begiven the same reference symbols, and explanation thereof will beomitted here.

[0460] The accumulating device 83 in which the condensers 82A through82E are connected in series as in Embodiments 7 through 9 has theproblem that a current flowing in and out of the condenser 11 affectsall of the condensers 82A through 82E when any of the switches 91through 96 is turned ON.

[0461] The present embodiment will explain a capacitive load drivecircuit that solves the above problem, with reference to FIG. 22.

[0462] As shown in FIG. 22, a capacitive load drive circuit 130 of thepresent embodiment has the same arrangement as the capacitive load drivecircuit 120 of Embodiment 9 except that an accumulating device 125 isprovided instead of the accumulating device 83.

[0463] In the accumulating device 125, one ends of condensers (energyaccumulating elements) 121 through 124 are connected to either the powersupply line 97 or the ground line 98, and the other ends of thecondensers 121 through 124 are connected to the switches 92 through 95to which the voltages V1 through V4, which are obtained by dividing thepower supply voltage VH, are applied. More specifically, the condenser121 is interposed between the ground line 98 and the switch 92, thecondenser 122 is interposed between the ground line 98 and the switch93, the condenser 123 is interposed between the power supply line 97 andthe switch 94, and the condenser 124 is interposed between the powersupply line 97 and the switch 95.

[0464] With this, when one of the switches 92 through 95 is selected,only one of the condensers 121 through 124 is connected to the condenser11. This separates the condensers 121 through 124 from one another,thereby preventing the condensers 121 through 124 from interfering withone another. In other words, when any of the switches 92 through 95 isswitched ON, the current flowing in and out of the condenser 11 affectsonly one of the condensers 121 through 124.

[0465] When the intermediate stages absorbs the difference between thepower supply voltage VH and the zener voltages as in Embodiments 9 and10, the number of stages for absorption, namely, the number of thecondensers 82A, 82B, 82C, 82D, and 82E interposed between the pulled-upline and the pulled-down line is not limited, but is preferably one.

[0466] Further, in the arrangement in which, as in Embodiments 9 and 10,the intermediate stages absorb the difference between the power supplyvoltage VH and the zener voltages, a difference between (i) the numberof zener diodes on the ground line 98 side, namely the number of zenerdiodes included in the first voltage divider 113A, and (ii) the numberof zener diodes on the power supply line 97 side, namely the number ofzener diodes included in the second voltage divider 113B is preferablyone or less, for better stability of the voltage.

[0467] Note that, Embodiments 7 through 10 explained the cases wherezener diodes are used as constant voltage means (constant voltageelement) for stabilizing the divided voltages, but other constantvoltage means (constant voltage element) such as a shunt regulator, forexample, may also be used instead of a zener diode.

[0468] [Embodiment 11]

[0469] The following will explain an embodiment of an ink-jet printer(image forming apparatus) employing the present invention, withreference to FIGS. 7, 23, and 24.

[0470]FIG. 23 is a perspective view showing chief members of the ink-jetprinter (image forming apparatus).

[0471] As shown in FIG. 23, an ink-jet printer (image forming apparatus)210 of the present embodiment is so arranged that a carriage 211, whichis connected to a pulse motor 213 via a timing belt 212, is guided by aguide member 214 to move back and forth in a direction of the width of arecording paper 215.

[0472] An ink-jet head 23 receives ink supplied from an ink cartridge217 which is placed on the carriage 211, and jets out ink drops onto therecording paper 215 so as to form dots on the recording paper 215 inaccordance with the motion of the carriage 211, thereby printing imagesand characters on the recording paper 215.

[0473]FIG. 24 is a cross-sectional view showing an arrangement of theink-jet head 23.

[0474] As shown in FIG. 24, the ink-jet head 23 is so arranged that anozzle plate 220 has a nozzle orifice 221; a flow path forming plate 222has (i) a communicating hole which partitions a pressure generatingchamber 223, (ii) a communicating hole or groove which partitions twoink supply ports that respectively communicate with the pressuregenerating chamber 223 on both sides, and (iii) a communicating holewhich partitions two common ink chambers 225 that respectivelycommunicate with the ink supply ports 224. A vibration plate 226 is madeof a thin plate that is elastically deformable. The vibration plate 226abuts on an edge of a piezoid 21 such as a piezoelectric element, and isso fixed that the vibration plate 226 and the nozzle plate 220 sandwichthe flow path forming plate 222, whereby the vibration plate 226 and theflow path forming plate 222 are integrated in a liquid-tight manner. Inthis way, a flow path unit 228 is constituted. The piezoid 21 is fixedon a fixed substrate 232.

[0475] With this arrangement, ink in the common ink chambers 225 flowinto the pressure generating chamber 223 via the ink supply ports 224,when the piezoid 21 contracts so as to expand the pressure generatingchamber 223. The ink in the pressure generating chamber 223 iscompressed so as to jet out ink drops through the nozzle orifice 221,when the piezoid 21 extends after a predetermined period so as tocontract the pressure generating chamber 223.

[0476] The piezoid 21 of the ink-jet head 23 is connected to thecapacitive load drive circuit 1 via the analog switch 22, as shown inFIG. 7. The capacitive load drive circuit 1 generates a trapezoidal waveof a voltage having a value required for jetting out ink drops throughthe nozzle orifice 221. Further, the analog switch 22 selectivelyapplies the output voltage V of the capacitive load drive circuit 1 tothe piezoid 21 which corresponds to data to be printed.

[0477] By using the capacitive load drive circuit 1 of the presentinvention to drive the piezoids of the ink-jet printer (image formingapparatus) 210 as described above, it is possible to reduce theelectrical power consumption of the ink-jet printer (image formingapparatus) 210.

[0478] Note that, the foregoing explained the case where the capacitiveload drive circuit of the present invention is used to drive thepiezoids (capacitive load) in the ink-jet printer (image formingapparatus) 210 which uses piezoids as ink jetting-out means forpressurizing ink to jet out the ink in droplets. However, the capacitiveload drive circuit of the present invention may also be used to driveelectrostatic drive electrodes in an ink-jet printer employing anelectrostatic method in which the electrostatic drive electrodes areused as the ink jetting-out means [such as a method to jet out ink usinginter-electrode electrostatic attraction force which is generated byapplying a voltage between two electrodes (electrostatic driveelectrodes)]. With this, the same effects of reducing electrical powerconsumption can be achieved.

[0479] Further, the ink-jet printer or image forming apparatus of thepresent invention is of course not limited to a special apparatus forprinting, but may be a complex machine having the functions of a copyingmachine, a facsimile machine, and the like.

[0480] [Embodiment 12]

[0481] Here, the principle of the present invention will be explained.

[0482] In a circuit of FIG. 50(a), it is assumed that an initialpotential of an energy accumulating element Cs1 is V0 and an initialpotential of the capacitive load Cd is 0, as shown in FIG. 50(a). Whenthe switch SW1 is switched ON at t=0, a potential difference between theenergy accumulating element Cs1 and the capacitive load Cd causes acurrent I to flow from the energy accumulating element Cs1 to thecapacitive load Cd, so as to charge the capacitive load Cd, as shown inFIG. 50(b). Here, the both terminal voltages of the capacitive load Cdare given by the following expression.$V = {\frac{Cs1}{{Cd} + {Cs1}} \cdot V_{0} \cdot \left\{ {1 - {{Exp}\left( {- \frac{t}{\tau \quad 1}} \right)}} \right\}}$${\tau 1} = {\frac{{Cd} \cdot {Cs1}}{{Cd} + {Cs1}} \cdot R}$

[0483] After the switch SW1 is kept turned ON for a sufficient time, thedifference between a voltage Vs of the energy accumulating element Cs1and a voltage Vd of the capacitive load Cd (potential difference betweenthe energy accumulating element Cs1 and the capacitive load Cd) iseliminated so that the current I becomes 0. FIGS. 51(a) and 51(b) showhow the voltages Vs and Vd and the current I change as time elapses.Here, V1 is the saturation voltage.$V_{1} = {\frac{Cs1}{{Cd} + {Cs1}} \cdot V_{0}}$

[0484] Next, the switch SW1 is turned OFF and the capacitive load Cd isconnected to an energy accumulating element Cs2 having an initialpotential of V0+ΔV (see FIG. 52). The potential difference between thecapacitive load Cd and the energy accumulating element Cs2 charges thecapacitive load Cd. Here, the both terminal voltages of the capacitiveload Cd are given by the following expression.$V = {{\frac{Cs2}{{Cd} + {Cs2}} \cdot \left( {V_{0} + {\Delta \quad V} - V_{1}} \right) \cdot \left\{ {1 - {{Exp}\left( {- \frac{t}{\tau \quad 2}} \right)}} \right\}} + V_{1}}$${\tau 2} = {\frac{{Cd} \cdot {Cs2}}{{Cd} + {Cs2}} \cdot R}$

[0485] After the switch SW2 is kept switched ON for a sufficient time,the potential difference between the energy accumulating element Cs1 andthe capacitive load Cd is eliminated so that the current I becomes 0(see FIG. 52). Here, V2 is the saturation voltage.$V_{2} = {{\frac{Cs2}{{Cd} + {Cs2}} \cdot \left( {V_{0} + {\Delta \quad V} - V_{1}} \right)} = V_{1}}$

[0486] Further, the switch SW2 is turned OFF and the switch SW1 isturned ON (see FIG. 53). The potential difference between the capacitiveload Cd and the energy accumulating element Cs2 discharges thecapacitive load Cd. Here, the both terminal voltages of the capacitiveload Cd are given by the following expression.$V = {{\frac{Cs1}{{Cd} + {Cs1}} \cdot \left( {V_{1} - V_{2}} \right) \cdot \left\{ {1 - {{Exp}\left( {- \frac{t}{\tau \quad 1}} \right)}} \right\}} + V_{2}}$

[0487] After the switch SW1 is kept switched ON for a sufficient time,the potential difference between the energy accumulating element Cs1 andthe capacitive load Cd is eliminated so that the current I becomes 0.Here, V3 is the saturation voltage.$V_{3} = {{\frac{Cs1}{{Cd} + {Cs1}} \cdot \left( {V_{1} - V_{2}} \right)} + V_{2}}$

[0488] Here, if it is assumed that the capacitance Cs1 of the energyaccumulating element Cs1 and the capacitance Cs2 of the energyaccumulating element Cs2 are sufficiently larger than the capacitance Cdof the capacitive load Cd, the following expressions are obtained.$\frac{Cs1}{{Cd} + {Cs1}} \approx {1\quad \frac{Cs2}{{Cd} + {Cs2}}} \approx 1$V₃ = V₁ = V₀

[0489] Therefore, in the energy accumulating element Cs1, (i) initialpotential V0, (ii) potential V1 after charging the capacitive load Cd,and (iii) potential V3 after being regenerated from the capacitive loadCd are approximately equivalent, so that apparent energy loss betweenthe energy accumulating element Cs1 and the capacitive load Cd becomes0.

[0490] Next, a capacitive load drive circuit 301 having four stages asshown in FIG. 30 will be exemplified as an embodiment to explain theprinciple of operation.

[0491] The capacitive load drive circuit 301 charges and discharges acapacitive load 311 such as a piezoid so as to drive the capacitive load311. The capacitive load drive circuit 301 is provided with condensersC(1), C(2), and C(3) as energy accumulating elements which are connectedin parallel between the capacitive load 311 and the ground. Thecapacitive load drive circuit 301 is further provided with an electricalpower source 309 which is an AC power source (power source) forsupplying the power supply voltage VH.

[0492] The capacitive load drive circuit 301 is provided with initialpotential applying means (not shown) for applying initial potentials(initial electric charge) respectively to the condensers C(1) throughC(3). The initial potential applying means splits (divides), into fourequal parts, a potential difference (voltage) between (i) the groundpotential (=0) and (ii) the power supply voltage VH which is suppliedfrom the electrical power source 309; and applies three potentials V1(=1/4·VH), V2 (=2/4·VH), and V3 (=3/4·VH), which are generated bydividing the voltage, respectively to the condensers C(1) through C(3)as the initial potentials. The initial potential applying means isconnected between the ground (ground point) and the electrical powersource 309, for example. The initial potential applying means is voltagedividing means which divides the potential difference between the groundpotential and the power supply voltage VH, and which supplies thedivided voltages to voltage dividing points to which the condensers C(1)through C(3) are respectively connected. For example, like the voltagedivider 5 as described before, the voltage dividing means may be aresistance type voltage dividing circuit having four resistors which areconnected in series between (i) the ground (ground terminal) and (ii) apower supplying point VH (power supply terminal) to which the powersupply voltage V is supplied.

[0493] Further, switching elements S(1), S(2), and S(3) are respectivelyconnected between the capacitive load 311 and the condensers C(1), C(2),and C(3). A switching element S(4) is connected between the electricalpower source 309 and the capacitive load 311. A switching element S(O)is connected between a ground potential G and the capacitive load 311.In this embodiment, the switching elements S(0) through S(4) make upswitching means. On the other hand, the other terminal of the capacitiveload 311, which is not connected to the switching elements S(0) throughS(4), is connected to the ground. Further, the other terminals of thecondensers C(1), C(2), and C(3), which are not connected to thecapacitive load 311, are connected to the ground via a ground point(reference potential terminal, ground terminal) C(0).

[0494] The following will explain the operation of the capacitive loaddrive circuit 301 as arranged above, with reference to FIGS. 31(a) to(e), 32(a) to 32(d), and 33. Note that, for convenience, the followingwill explain a case where the power supply voltage VH is a positivepotential. When the power supply voltage VH is a negative potential, thecapacitive load drive circuit 301 operates in the same manner exceptthat the potential has the opposite polarity and the electric chargemoves in the opposite direction.

[0495] Initially, only the switching element S(0) is switched ON (ONstate) among the switching elements S(0) through S(4), as shown in FIG.31(a); and the capacitive load 311 does not accumulate electric charge(initial state) (S0 in FIG. 81).

[0496] In a first step, the switching element S(0) is switched OFF (OFFstate), and then the switching element S(1) is switched ON, as shown inFIG. 31(b). Here, the condenser C(1) accumulates energy of the potentialV1 (=1/4·VH), and the capacitive load 311 does not accumulate electriccharge, resulting in a potential difference of VH/4 between thecondenser C(1) and the capacitive load 311. With this potentialdifference of VH/4, electric charge in accordance with a ratio of acapacitance C1 of the condenser C(1) to the capacitance Cd of thecapacitive load 311 moves from the condenser C(1) to the capacitive load311. In other words, the condenser C(1) supplies electrostatic energy(hereinafter merely referred to as “energy” when appropriate) to thecapacitive load 311, so as to charge the capacitive load 311 (S1 in FIG.81). The potential of the condenser C(1) falls as much as an amount ofelectric charge flowing into the capacitive load 311, whereas thepotential of the capacitive load 311 rises by an amount of electriccharge flowing from the condenser C(1). When the capacitance C1 of thecondenser C(1) is sufficiently larger than the capacitance Cd of thecapacitive load 311 (C1>Cd), the change in potential of the condenserC(1) is small. When the switching element S(1) is kept switched ON for asufficiently long time, the condenser C(1) and the capacitive load 311have substantially the same potential as a result of the energytransfer. Consequently, the potentials of the condenser C(1) and thecapacitive load 311 after charging are slightly lower than the initialpotential VH/4 (=V1) of the condenser C(1) (see FIG. 33). This potentialafter charging is V1′.

[0497] In a second step, the switching element S(1) is switched OFF, andthen the switching element S(2) is switched ON, as shown in FIG. 31(c).Here, the condenser C(2) accumulates energy of the potential V2 which ishigher than the potential V1′, so that electric charge in accordancewith a ratio of a capacitance C2 of the condenser C(2) to thecapacitance Cd of the capacitive load 311 moves from the condenser C(2)to the capacitive load 311. In other words, with the potentialdifference V2−V1′ (=VH/4+α;α is a positive value extremely smaller thanVH), the condenser C(2) supplies energy to the capacitive load 311, soas to further charge the capacitive load 311 (S2 in FIG. 81). Thepotential of the condenser C(2) falls as much as an amount of electriccharge flowing into the capacitive load 311, whereas the potential ofthe capacitive load 311 rises by an amount of electric charge flowingfrom the condenser C(2). When the capacitance C2 of the condenser C(2)is sufficiently larger than the capacitance Cd of the capacitive load311 (C2>Cd), the change in potential of the condenser C(2) is small.When the switching element S(2) is kept switched ON for a sufficientlylong time, the condenser C(2) and the capacitive load 311 havesubstantially the same potential as a result of the energy transfer.Consequently, the potentials of the condenser C(2) and the capacitiveload 311 after charging are slightly lower than the initial potential2VH/4 (=V2) of the condenser C(2) (see FIG. 33). This potential aftercharging is V2′.

[0498] In a third step, the switching element S(2) is switched OFF, andthen the switching element S(3) is switched ON, as shown in FIG. 31(d).Here, the condenser C(3) accumulates energy of the potential V3 which ishigher than the potential V2′, so that electric charge in accordancewith a ratio of a capacitance C3 of the condenser C(3) to thecapacitance Cd of the capacitive load 311 moves from the condenser C(3)to the capacitive load 311. In other words, with the potentialdifference V3−V2′ (=VH/4+α), the condenser C(3) supplies energy to thecapacitive load 311, so as to further charge the capacitive load 311 (S3in FIG. 81). The potential of the condenser C(3) falls as much as anamount of electric charge flowing into the capacitive load 311, whereasthe potential of the capacitive load 311 rises by an amount of electriccharge flowing from the condenser C(3). When the capacitance C3 of thecondenser C(3) is sufficiently larger than the capacitance Cd of thecapacitive load 311 (C3>Cd), the change in potential of the condenserC(3) is small. When the switching element S(3) is kept switched ON for asufficiently long time, the condenser C(3) and the capacitive load 311have substantially the same potential as a result of the energytransfer. Consequently, the potentials of the condenser C(3) and thecapacitive load 311 after charging are slightly lower than the initialpotential 3VH/4 (=V3) of the condenser C(3) (see FIG. 33). Thispotential after charging is V3′.

[0499] In a fourth step, the switching element S(3) is switched OFF, andthen the switching element S(4) is switched ON, as shown in FIG. 31(e).Here, the power supply voltage (power supply potential) VH is higherthan the potential V3′. With this potential difference VH-V3′(=VH/4+α),the electrical power source 309 supplies energy to the capacitive load311, so as to further charge the capacitive load 311 (S4 in FIG. 81).When the switching element S(4) is kept switched ON for a sufficientlylong time, the potential of the capacitive load 311 after charging isboosted to the power supply voltage VH.

[0500] In a fifth step, the switching element S(4) is switched OFF, andthen the switching element S(3) is switched ON, as shown in FIG. 32(a)(S5 in FIG. 81). Here, the capacitive load 311 accumulates VH, which ishigher than the potential V3′ of the condenser C(3). With this potentialdifference of VH-V3′, which is VH/4+α, electric charge in accordancewith a ratio of the capacitance C3 of the condenser C(3) to thecapacitance Cd of the capacitive load moves to the condenser C(3). Withthis, the potential of the condenser C(3) rises by an amount of electriccharge flowing from the capacitive load 311, whereas the potential ofthe capacitive load 311 falls as much as an amount of electric chargeflowing into the condenser C(3). When the switching element S(3) is keptswitched ON for a sufficiently long time, the condenser C(3) and thecapacitive load 311 have the same potential as a result of the energytransfer. Consequently, the potential of the condenser C(3)substantially returns to the original V3=3VH/4, namely, energy isregenerated from the capacitive load 311 to the condenser C(3) (S5 inFIG. 81).

[0501] In a sixth step, the switching element S(3) is switched OFF, andthen the switching element S(2) is switched ON, as shown in FIG. 32(b)(S6 in FIG. 81). Here, the capacitive load 311 accumulates V3, which ishigher than the potential V2′. With this potential difference of V3−V2′,which is VH/4+α, electric charge in accordance with a ratio of thecapacitance C2 of the condenser C(2) to the capacitance Cd of thecapacitive load 311 moves from the capacitive load 311 to the condenserC(2), so as to charge the condenser C(2). With this, the potential ofthe condenser C(2) rises by an amount of electric charge flowing fromthe capacitive load 311, whereas the potential of the capacitive load311 falls as much as an amount of electric charge flowing into thecondenser C(2). When the switching element S(2) is kept switched ON fora sufficiently long time, the condenser C(2) and the capacitive load 311have the same potential as a result of the energy transfer.Consequently, the potential of the condenser C(2) substantially returnsto the original V2=2VH/4. Namely, energy is regenerated from thecapacitive load 311 to the condenser C(2) (S6 in FIG. 81).

[0502] In a seventh step, the switching element S(2) is switched OFF,and then the switching element S(1) is switched ON, as shown in FIG.32(c) (S7 in FIG. 81). Here, the capacitive load 311 accumulates energyof the potential V2, which is higher than the potential V1′. With thispotential difference of V2−V1′, which is VH/4+α, electric charge inaccordance with a ratio of the capacitance C1 of the condenser C(1) tothe capacitance Cd of the capacitive load 311 moves from the capacitiveload 311 to the condenser C(1), so as to charge the condenser C(1). Withthis, the potential of the condenser C(1) rises by an amount of electriccharge flowing from the capacitive load 311, whereas the potential ofthe capacitive load 311 falls as much as an amount of electric chargeflowing into the condenser C(1). When the switching element S(1) is keptswitched ON for a sufficiently long time, the condenser C(1) and thecapacitive load 311 have the same potential as a result of the energytransfer. Consequently, the potential of the condenser C(1)substantially returns to the original V1=VH/4. Namely, energy isregenerated from the capacitive load 311 to the condenser C(1) (S7 inFIG. 81).

[0503] In an eighth step, the switching element S(1) is switched OFF,and then the switching element S(2) is switched ON, as shown in FIG.32(d). Here, the capacitive load 311 accumulates energy of the potentialV1′, which is higher than the ground potential'. With this potentialdifference of V1′, which is the potential difference of VH/4+α, electriccharge of the capacitive load 311 flows out (is discharged) to theground potential, namely, is consumed (discarded) (S8 in FIG. 81). Afterthis, the capacitive load drive circuit 301 resumes S1.

[0504] As described above, in terms of energy during the first througheighth steps S1 through S8, the energy accumulated in the condenser C(1)which is supplied into the capacitive load 311 in the first step S1 isregenerated by the energy sent back to the condenser C(1) from thecapacitive load 311 in the seventh step S7. The energy supplied to thecapacitive load 311 in the second step S2 is regenerated by the energysent back to the condenser C(1) from the capacitive load 311 in thesixth step S6. The energy supplied to the capacitive load 311 in thethird step S3 is regenerated by the energy sent back to the condenserC(1) from the capacitive load 311 in the fifth step S5. In summary,during the first through eighth steps S1 through S8, energy is suppliedto the capacitive load 311 in the fourth step S4, energy is consumed inthe eighth step S8, and energy transfer in the remaining steps isrespectively canceled out between paired steps (see FIG. 33). Therefore,energy is not apparently supplied or consumed. As a result, consumed isonly energy corresponding to 1/4·VH equivalently. In other words, it ispossible to charge and discharge the capacitive load 311 while consuming25% of energy that is consumed in a method such as the Push-Pull methodwhich consumes the voltage VH to charge and discharge the capacitiveload.

[0505] More specifically, the following will describe how the voltageschange when the capacitive load drive circuit 301 having four stages isused to generate a pulse whose crest value is 10 Vpp. When 10V isdivided by four, 10V is divided into five potentials, namely 2.5V, 5.0V,and 7.5V of the respective potentials of the condensers C(1) throughC(3), 0V of the ground potential, and 10V of the power supply potential,at a potential difference of 2.5V between each stage. Further, thecapacitance of the condensers C(1) through C(3) is preferably largerthan the capacitance of the capacitive load 311. To make the operationeasily understandable, it is assumed here that the capacitance of thecondensers C(1) through C(3) is four times greater than the capacitanceof the capacitive load 311. Further, each of the switching elements S(0)through S(4) used in the system is generally a semiconductor switch suchas a half-FET (field effect transistor) and a GTO thyristor. Thesemiconductor switch charges and discharges the capacitive load 311exponentially with a particular time constant, because the semiconductorswitch has a considerable ON resistance. Accordingly, the relationshipbetween (i) the time during which the switching elements S(0) throughS(4) are ON and (ii) the time constant of charging and discharging thecapacitive load 311 becomes important when forming a waveform. Forsimplicity, the calculation is performed here by assuming that the ONresistances of the switching elements S(0) through S(4) are very small,and the switching elements S(0) through S(4) are switched from one stageto another after a sufficiently long switching time to the degree thatthe influence of the ON resistances of the switching elements S(0)through S(4) are negligible in the system. Table 1shows the results ofthe calculation. In Table 1, Vd is the potential of the capacitive load311, Vs_(—)0 is the ground potential, Vs_n (n=1 through 3) is thepotential of the condenser C(n) at each stage, and Vs_(—)4 is the powersupply potential. TABLE 1 Vs_4 Vs_3 Vs_2 Vs_1 Vs_0 Vd 10.0 7.5 5.0 2.50.0 0.0 INITIAL STATE (S0) 10.0 7.5 5.0 2.0 0.0 2.0 AFTER THE FIRST STEPS1 10.0 7.5 4.4 2.0 0.0 4.4 AFTER THE SECOND STEP S2 10.0 6.9 4.4 2.00.0 6.9 AFTER THE THIRD STEP S3 10.0 6.9 4.4 2.0 0.0 10.0 AFTER THEFOURTH STEP S4 10.0 7.5 4.4 2.0 0.0 7.5 AFTER THE FIFTH STEP S5 10.0 7.55.0 2.0 0.0 5.0 AFTER THE SIXTH STEP S6 10.0 7.5 5.0 2.5 0.0 2.5 AFTERTHE SEVENTH STEP S7 10.0 7.5 5.0 2.5 0.0 0.0 AFTER THE EIGHTH STEP S8

[0506] As can be seen from the results, the potential of each condenserdecreases when each condenser supplies energy into the capacitive load.However, the potential of each condenser is restored when the capacitiveload supplies energy back to each condenser. As a result, the electricalpower is regenerated.

[0507] As described above, the capacitive load drive circuit 301 of thepresent embodiment is arranged so as to include a power supply terminal309 a to which a power supply voltage VH is applied from an electricalpower source 309; a ground terminal C(0) (reference potential terminal)to which a ground potential (reference potential) is applied; threecondensers C(1) through C(3) to which initial potentials V(1) throughV(3) are respectively applied, the initial potentials V(1) through V(3)being different from one another and being between the ground potentialand the power supply voltage VH; and switching elements S(0) throughS(4) for selectively connecting the capacitive load 311 with the groundterminal C(0), the condensers C(1) through C(3), and the power supplyterminal 309 a, the switching elements S(0) through S(4) carrying outthe steps of (i) connecting the capacitive load 311 with the groundterminal C(0) and then sequentially connecting the capacitive load 311with the condensers C(1) through C(3) in an order of the initialpotentials from the initial potential that is closest to the groundpotential so as to change a terminal voltage of the capacitive load 311toward the power supply potential VH (S1 through S3), (ii) selectivelyconnecting the capacitive load 311 with the power supply terminal 309 aso as to increase an absolute value of the terminal voltage of thecapacitive load 311 (S4), and (iii) sequentially connecting thecapacitive load 311 with the condensers C(1) through C(3) in an order ofthe initial potentials from the initial potential that is closest to thepower supply potential VH so as to decrease the absolute value of theterminal voltage of the capacitive load 311 and so as to regenerateelectrostatic energy to be accumulated in the condensers C(1) throughC(3), the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the condensers C(1)through C(3) before the step (i) (S5 through S7), the steps (i) through(iii) being carried out in this order.

[0508] Note that, the foregoing described the case where the number ofthe condensers to which initial potentials are respectively applied arethree, the initial potentials being different from one another and beingbetween the ground potential and the power supply voltage VH, and thenumber of steps of charging (or discharging) the capacitive load 311(which is smaller than the number of kinds of potentials of theswitching elements S(0) through S(4) by one, and which is larger thanthe number of condensers by one; hereinafter referred to as “the numberof stages”) is four.

[0509] However, the number of stages is not particularly limited,provided that the number of stages is two or more. Ideally, theregeneration efficiency improves as the number of stages increases. Forexample, the regeneration efficiency is 50% with two stages, theregeneration efficiency is 66.7% with three stages, the regenerationefficiency is 75% with four stages, and the regeneration efficiency is80% with five stages. However, as the number of stages increases, a risetime for the voltage becomes longer, and the number of required circuitsbecomes larger. Accordingly, the number of stages may be determineddepending on a required waveform of the drive pulse, the size of thecircuit, cost, and the like. Generally, the circuit is preferablyarranged to have three to four stages when the voltage is required torise quickly; whereas the circuit is preferably arranged to have four tofive stages so as to reduce electrical power consumption.

[0510] Further, the foregoing described the case where the power supplyvoltage VH is equally divided by four stages, but it is not necessarythat the power supply voltage VH is equally divided. However, thecapacitive load drive circuit 301 of the present embodiment regenerateselectrical power using the principle in which (A) energy which isreduced in the condenser (I) by supplying energy from the condenser C(I)(I=1, 2, 3) to the capacitive load 311 whose potential is V(I-1) (whereV(0)=0) (S1 through S3) is regenerated by supplying (B) energy to C(I)from the capacitive load 311 whose potential is V(I) (where V(4)=VH) (S5through S8). Accordingly, it is most preferable to equally divide theelectrical power voltage VH, for ideally regenerating electrical power.

[0511] Here, the time constant of the capacitive load 311 and theswitching time of the condenser C(I) will be discussed.

[0512] In the circuit shown in FIG. 54, first, it is assumed that theinitial potential is applied to the condenser Cs, and the capacitiveload Cd is discharged. Here, after the switch SW is turned ON, thevoltage of the capacitive load Cd increases as time elapses, as shown inFIG. 55. After a sufficient time, the potential difference between thecapacitive load Cd and the condenser Cs is eliminated so that thecurrent I becomes 0. This saturation voltage will be referred to as“attainment voltage” in the present specification.

[0513] In the circuit shown in FIG. 54, it is assumed that the switch isturned OFF after a particular time (switching time (Ts)). When theswitching time (Ts) is shorter than the time constant (τo=R·Cd, where Ris an DC resistive component of the charge or discharge path includingthe energy accumulating elements and the capacitive load, and Cd is thecapacitance of the capacitive load), the voltage of the capacitive loadCd changes as shown in FIG. 56(a). Accordingly, the voltage of thecapacitive load Cd changes as shown in FIG. 56(b) in the capacitive loaddrive circuit having three stages in accordance with the presentinvention.

[0514] When the switching time (Ts) is equal to the time constant(τo=R·Cd), the voltage of the capacitive load Cd changes as shown inFIG. 57(a). Accordingly, the voltage of the capacitive load Cd changesas shown in FIG. 57(b) in the capacitive load drive circuit having threestages in accordance with the present invention.

[0515] When the switching time (Ts) is longer than the time constant(τo=R·Cd), the voltage of the capacitive load Cd changes as shown inFIG. 58(a). Accordingly, the voltage of the capacitive load Cd changesas shown in FIG. 58(b) in the capacitive load drive circuit having threestages in accordance with the present invention.

[0516] The capacitive load drive circuit of the present inventionpreferably satisfies the following expression:

[0517] τo≦Ts≦2.5·τo(τo =R·Cd),

[0518] where Cs is the capacitive component of the energy accumulatingelements, Cd is the capacitance of the capacitive load, R is a DCresistive component of the charge or discharge path including the energyaccumulating elements and the capacitive load, and Ts is the time forswitching the energy accumulating elements (switching time; a time to bekept connected to the capacitive load). When Ts<τo, the crest value ofthe obtained pulse is not more than 63% of the attainment voltage,thereby lowering the efficiency in supplying energy to the capacitiveload. When Ts>2.5τo, the switching time becomes extremely long.

[0519] [Embodiment 13]

[0520] Next, the following will explain still another embodiment of thepresent invention with reference to FIGS. 34, 35(a) to 35(f), 36, and37. Note that, for convenience, members having the same functions asthose used in Embodiment 12 will be given the same reference symbols,and explanation thereof will be omitted here.

[0521] A capacitive load drive circuit 302 of the present embodiment isdifferent from the capacitive load drive circuit 301 of Embodiment 12 inthat a condenser C(N) is additionally provided between the electricalpower source 309 and the switching element S(4) which is connected tothe electrical power source 309, and the number of stages (number ofcondensers) is generalized.

[0522] As shown in FIGS. 34 and 35, the capacitive load drive circuit302 of the present embodiment is a pulse generating circuit whichincludes a ground terminal C(0) having a ground potential (referencepotential) V(0) (=0); N condensers C(1) through C(N) (energyaccumulating elements) having initial potentials V(1) through V(N) whichare not 0 (N is a natural number not less than 2), the condenser C(N)connecting to an electrical power generating source (directly or via acircuit); a switching element S(0) (switching means) for connecting thecapacitive load 311 with the ground terminal C(0) (reference potentialterminal); and N switching elements S(1) through S(N) for selectivelyconnecting the capacitive load 311 with the condensers C(1) through C(N)(switching means), one of the N condensers C(1) through C(N) being acondenser C(I) (first energy accumulating element) having a firstinitial potential V(I) which is not 0, one of the N condensers C(1)through C(N) being a condenser C(I+1) (second energy accumulatingelement) having a second initial potential V(I+1) which has the samepolarity as the initial potential V(I) and which has a larger absolutevalue than the initial potential V(I), the switching elements S(0)through S(N) (switching means) carrying out (i) a first charging step ofselectively connecting the capacitive load 311 with the ground terminalor the condenser C(I−1) (ground terminal or third energy accumulatingelement) and then selectively connecting the capacitive load 311 withthe condenser C(I) so as to change a potential (terminal voltage) of thecapacitive load 311 toward the initial potential of the condenser C(I);(ii) a second charging step of selectively connecting the capacitiveload 311 with the condenser C(I+1) so as to increase an absolute valueof the potential (terminal voltage) of the capacitive load 311; and(iii) a discharging step of selectively connecting the capacitive load311 with the condenser C(I) so as to decrease the absolute value of thepotential (terminal voltage) of the capacitive load 311 and so as toregenerate electrostatic energy to be accumulated in the condenser C(I),the thus regenerated electrostatic energy being approximately equal toelectrostatic energy as accumulated in the condenser C(I) before thestep (i), the steps (i) through (iii) being carried out in this order.Note that, the circuit for supplying initial electric charge is omittedin FIG. 34.

[0523] The operation of the above arrangement will be explained withreference to FIGS. 35(a) through 35(f).

[0524] When generating a pulse, energy is consumed in such a manner thatelectric charge which moves from the condenser C(N) to the condenserC(N−1) is transferred toward the ground potential so as to be consumedat the ground terminal C(0). The cycle of FIG. 35(a) through FIG. 35(f)achieves the same effects as the cycle of the steps S1 through S8 inEmbodiment 12. In other words, by making (A) the electric charge flowingout of the condenser C(I) between FIGS. 35(a) and 35(b) to beapproximately equal to (B) the electric charge flowing into thecondenser C(I) between FIGS. 35(d) and 35(e), the condenser C(I) doesnot apparently consume energy during the cycle of FIGS. 35(a) through35(f).

[0525] Thus, the capacitive load drive circuit may be arranged to carryout at least the cycle of FIGS. 35(a) through 35(f), and use all of theN condensers C(1) through C(N) or a part of the N condensers C(1)through C(N). The condensers may be appropriately used in accordancewith a pulse to be generated. For example, all of the condensers C(1)through C(N) may be used to generate a pulse whose base potential is theground potential and whose pulse amplitude is wide. Further, only a partof the condensers may be used to generate a pulse having a lower crestvalue than the power supply voltage VH or to generate a pulse whose basepotential is not the ground potential.

[0526] Therefore, the capacitive load drive circuit 302 of the presentembodiment may be arranged so as to include a plurality of condensersC(1) through C(N) to which a plurality of different initial potentialsV(1) through V(N) (N is a natural number not less than 2) are applied;and switching elements S(1) through S(N) for selectively connecting thecapacitive load 311 with the condensers C(1) through C(N), one of theplurality of condensers C(1) through C(N) being a condenser C(I) havinga first initial potential V(I) which is not 0, one of the plurality ofcondensers C(1) through C(N) being a condenser C(I+1) having a secondinitial potential V(I+1) which has a larger absolute value than theinitial potential V(I), one of the plurality of condensers C(1) throughC(N) being a condenser C(I−1) having a third initial potential V(I−1)which has the same polarity as the first initial potential V(I) andwhich has a smaller absolute value than the first initial potentialV(I), the switching elements S(0) through S(N) carrying out (i) a firstcharging step of selectively connecting the capacitive load 311 with thecondenser C(I−1) and then selectively connecting the capacitive load 311with the condenser C(I) so as to change a terminal voltage 311 of thecapacitive load toward the first initial potential; (ii) a secondcharging step of selectively connecting the capacitive load 311 with thesecond initial potential V(I+1) and an energy accumulating element so asto increase an absolute value of the terminal voltage of the capacitiveload 311, and (iii) a discharging step of selectively connecting thecapacitive load 311 with the condenser C(I) so as to decrease theabsolute value of the terminal voltage of the capacitive load 311 and soas to regenerate electrostatic energy to be accumulated in the firstcondenser C(I), the thus regenerated electrostatic energy beingapproximately equal to electrostatic energy as accumulated in the firstcondenser C(I) before the step (i), the steps (i) through (iii) beingcarried out in this order.

[0527] Further, the initial potentials V(1) through V(N) may be positiveor negative. A pulse as shown in FIG. 36, for example, can be generatedwhen the initial potentials V(1) through V(N) are positive. A pulse asshown in FIG. 37, for example, can be generated when the initialpotentials V(1) through V(N) are negative.

[0528] Note that, the capacitive load drive circuit can operate withoutthe condenser C(N) which is connected to the electrical power source 309in the present embodiment (the condenser C(N) is generally integrated inthe electrical power source 309).

[0529] Therefore, the capacitive load drive circuit 302 of the presentembodiment may be arranged so as to include a power supply terminal (VH)to which a power supply potential VH is applied form an electrical powersource 309; N condensers C(1) through C(N) to which a plurality ofdifferent initial potentials V(1) through V(N) (N is a natural numbernot less than 2) are applied; and switching elements S(1) through S(N)for selectively connecting the capacitive load 311 with the condensersC(1) through C(N) and the power supply terminal (VH), the condensersC(1) through C(N) including a condenser C(I) having a first initialpotential V(I) which has the same polarity as the power supply potentialVH and which has a smaller absolute value than the power supplypotential VH, and a condenser C(I−1) having a third initial potentialV(I−1) which has the same polarity as the first initial potential V(I)and has a smaller absolute value than the first initial potential V(I),the switching elements S(0) through S(N) carrying out (i) a firstcharging step of selectively connecting the capacitive load 311 with thecondenser C(I−1) and then selectively connecting the capacitive load 311with the condenser C(I) so as to change a terminal voltage of thecapacitive load 311 toward the first initial potential V(I); (ii) asecond charging step of selectively connecting the capacitive load 311with the power supply terminal (VH) so as to increase an absolute valueof the terminal voltage of the capacitive load 311, and (iii) adischarging step of selectively connecting the capacitive load 311 withthe condenser C(I) so as to decrease the absolute value of the terminalvoltage of the capacitive load 311 and so as to regenerate electrostaticenergy to be accumulated in the condenser C(I), the thus regeneratedelectrostatic energy being approximately equal to electrostatic energyas accumulated in the condenser C(I) before the step (i), the steps (i)through (iii) being carried out in this order.

[0530] Next, the following will discuss how to set the capacitivecomponents of the condensers C(1) through C(3), the capacitance of thecapacitive load 311, the switching time of the switching elements S(1)through S(3), and the resistance value of the charge and dischargepaths, in the capacitive load drive circuit 301 having four stages asshown in FIG. 30. It is considered to be desirable that the voltage ofthe capacitive load 311 reaches 90% of the attainment voltage (finalvoltage attained by the capacitive load 311 after repeating the firstthrough third steps infinitely) during the first through third steps.Thus, the conditions for achieving this result will be discussed.

[0531] First, it is assumed that a switching time of the switchingelement S(1) is a time of the first step, a switching time of theswitching element S(2) is a time of the second step, and a switchingtime of the switching element S(3) is a time of the third step, whichare all equivalent to one another.

[0532] Here, the time constant τ0 (unit sec) for charging anddischarging each of the condensers C(1) through C(3) is given by thefollowing expression:

τ0=R·Cd,

[0533] where Cd (unit F) is the capacitance of the capacitive load 311,R (unit Ω) is the resistance value of the charge and discharge paths ofeach of the condensers C(1) through C(3) with respect to the capacitiveload 311. When Cs (unit F) is the capacitive component of the condensersC(1) through C(3), X is the load capacitance ratio Cd/Cs, and Ts (unitsec) is the switching time of the switching elements S(1) through S(3),the condition that causes the voltage of the capacitive load 311 toreach 90% of the attainment voltage during the first through third stepswas obtained through theoretical calculation, as indicated by the solidline in FIG. 82. FIG. 82 shows the maximum load capacitance ratio X(=Cd/Cs) that causes the voltage of the capacitive load 311 to be notless than 90% of the attainment voltage during the first through thirdsteps, with respect to a ratio Ts/τ0 of the time constant τ0 to theswitching time Ts.

[0534] As shown in FIG. 82, when Ts/τ0<2.5, the condition that causesthe voltage of the capacitive load 311 to reach 90% of the attainmentvoltage during the first through third steps is approximately equal tothe following approximated curve.

X=0.164(Ts/τ0)^(0.2198)

[0535] On the other hand, when Ts/τ0≧2.5, the condition that causes thevoltage of the capacitive load 311 to reach 90% of the attainmentvoltage during the first through third steps is approximately equal tothe following straight line.

X=0.2

[0536] Consequently, the conditions that cause the voltage of thecapacitive load 311 to reach 90% of the attainment voltage during thefirst through third steps are approximately expressed as follows:

when Ts/(R·Cd)<2.5,

Cd/Cs≦0.164{Ts/(R·Cd)}^(0.2198;)

when Ts/(R·Cd)≧2.5,

Cd/Cs≦0.2.

[0537] Therefore, when the foregoing conditions are satisfied, thecapacitive load 311 can obtain not less than 90% of the attainmentvoltage during the first through third steps. When the above expressionsare not satisfied, the voltages of the condensers C(1) through C(3)change more widely due to the electric charge flowing out of thecondensers C(1) through C(3) to the capacitive load 311. As a result,the voltage of the capacitive load 311 does not reach 90% of theattainment voltage during the first through third steps. Thisdeteriorates the power regeneration ratio in generating pulses, therebypreventing the energy-saving driving of the capacitive load drivecircuit. Further, when the above expressions are not satisfied, thevoltages of C(1) through C(3) widely change when generating one pulse,requiring that the changes in the voltages be corrected beforegenerating the next pulse.

[0538] The foregoing described the examination of the conditions thatcause the voltage of the capacitive load 311 to reach 90% of theattainment voltage during the first through third steps. Anotherimportant aspect is to improve the energy regeneration ratio.

[0539] In the capacitive load drive circuit 301 having four stages asshown in FIG. 30, the time constant τ0 (unit sec) for charging anddischarging each of the condensers C(1) through C(3) is given by thefollowing expression:

τ0=R·Cd,

[0540] where Cd (unit F) is the capacitance of the capacitive load 311,R (unit Ω) is the resistance value of the charge and discharge paths ofeach of the condensers C(1) through C(3) with respect to the capacitiveload 311. When Cs (unit F) is the capacitive component of the condensersC(1) through C(3), X is the load capacitance ratio Cd/Cs, and Ts (unitsec) is the switching time of the switching elements S(1) through S(3),theoretical calculation gave how an energy consumption ratio (equal to avalue obtained by subtracting the energy regeneration ratio from 1)changes with respect to the ratio Ts/τ0 of the time constant τ0 to theswitching time Ts when the load capacitance ratio X varies from 0.003 to0.3, as shown in FIG. 85.

[0541] Further, FIG. 83 shows how the energy consumption ratio changeswith respect to the ratio Ts/τ0 of the time constant τ0 to the switchingtime Ts when the load capacitance ratio X varies from 0.003 to 0.3 in acapacitive load drive circuit having two stages, which is different fromthe capacitive load drive circuit 301 of FIG. 30 having four stages onlyin the number of stages.

[0542] Further, FIG. 84 shows how the energy consumption ratio changeswith respect to the ratio Ts/τ0 of the time constant τ0 to the switchingtime Ts when the load capacitance ratio X varies from 0.003 to 0.3 in acapacitive load drive circuit having three stages, which is differentfrom the capacitive load drive circuit 301 of FIG. 30 having four stagesonly in the number of stages.

[0543] Further, FIG. 86 shows how the energy consumption ratio changeswith respect to the ratio Ts/τ0 of the time constant τ0 to the switchingtime Ts when the load capacitance ratio X varies from 0.003 to 0.3 in acapacitive load drive circuit having five stages, which is differentfrom the capacitive load drive circuit 301 of FIG. 30 having four stagesonly in the number of stages.

[0544] Further, FIG. 87 shows how the energy consumption ratio changeswith respect to the ratio Ts/τ0 of the time constant τ0 to the switchingtime Ts when the load capacitance ratio X varies from 0.003 to 0.3 in acapacitive load drive circuit having six stages, which is different fromthe capacitive load drive circuit 301 of FIG. 30 having four stages onlyin the number of stages. Note that, when the load capacitance ratio X is0.001 (which is not shown in FIGS. 83 through 87), the energyconsumption ratio changes approximately in the same manner as in thecase where the load capacitance ratio X is 0.003.

[0545] These results revealed that, through the energy consumption ratiolargely depends on Ts/τ0, it is possible to sufficiently lower theenergy consumption ratio in spite of the increase in the capacitance Cdof the capacitive load if the load capacitance ratio X satisfies thefollowing expression.

X≦0.01

[0546] When the above expression is satisfied, it is possible toeffectively supply the output voltages of the condensers to thecapacitive load 311 without reducing the output voltages of thecondensers. Further, when X≦0.01, it is possible to reduce changes inthe drive voltage caused by unevenness and changes (temperature changes,and the like) in the capacitance of the condensers or capacitive load.This can realize highly reliable jetting-out operation, thereby stablyoperating the drive system (system driven by the capacitive load drivecircuit) including the capacitive load 311. In contrast, when the aboveexpression is not satisfied, the energy regeneration ratio lowers whenthe capacitance Cd of the capacitive load increases.

[0547] Next, the conditions that achieve a good slew rate of a waveformof a pulse to be applied to the capacitive load (10% to 90%) (amount ofvoltage change when the pulse rises from a crest value of 10% to 90%,with respect to a time required for the pulse to rise from the crestvalue of 10% to 90%) will be discussed.

[0548] In the capacitive load drive circuit 301 having four stages asshown in FIG. 30, the time constant τ0 (unit sec) for charging anddischarging each of the condensers C(1) through C(3) is given by thefollowing expression:

τ0=R·Cd,

[0549] where Cd (unit F) is the capacitance of the capacitive load 311,R (unit Ω) is the resistance value of the charge and discharge paths ofeach of the condensers C(1) through C(3) with respect to the capacitiveload 311. Then, it is assumed that Cs (unit F) is the capacitivecomponent of the condensers C(1) through C(3), Ts (unit sec) is theswitching time of the switching elements S(1) through S(3), V (=3VH/4)is a final attainment voltage (voltage attained by the capacitive load311 after charged by the condensers C(1) through C(3) for an infinitetime), SR (unit V/μsec) is a slew rate (10% to 90%) of a waveform of apulse to be applied to the capacitive load 311, and:

x=Ts/τ0.

[0550] With this, theoretical calculation gave how a slew rate (10% to90%) SR changes with respect to the ratio x=Ts/τ0 of the time constantτ0 to the switching time Ts when the load capacitance ratio X variesfrom 0.001 to 0.3, as shown in FIG. 90. Note that, when the loadcapacitance ratio X is 0.003 to 0.03 (which is not shown in FIG. 90),the slew rate (10% to 90%) SR changes approximately in the same manneras in the case where the load capacitance ratio X is 0.001.

[0551] Further, FIG. 88 shows how the slew rate (10% to 90%) SR changeswith respect to the ratio x=Ts/τ0 of the time constant τ0 to theswitching time Ts when the load capacitance ratio X varies from 0.001 to0.1 in a capacitive load drive circuit having two stages, which isdifferent from the capacitive load drive circuit 301 having four stagesof FIG. 30 only in the number of stages. Note that, when the loadcapacitance ratio X is 0.003 (which is not shown in FIG. 88), the slewrate (10% to 90%) SR changes approximately in the same manner as in thecase where the load capacitance ratio X is 0.001.

[0552] Further, FIG. 89 shows how the slew rate (10% to 90%) SR changeswith respect to the ratio x=Ts/τ0 of the time constant τ0 to theswitching time Ts when the load capacitance ratio X varies from 0.001 to0.1 in a capacitive load drive circuit having three stages, which isdifferent from the capacitive load drive circuit 301 having four stagesof FIG. 30 only in the number of stages. Note that, when the loadcapacitance ratio X is 0.003 to 0.01 (which is not shown in FIG. 89),the slew rate (10% to 90%) SR changes approximately in the same manneras in the case where the load capacitance ratio X is 0.001.

[0553] Further, FIG. 91 shows how the slew rate (10% to 90%) SR changeswith respect to the ratio x=Ts/τ0 of the time constant τ0 to theswitching time Ts when the load capacitance ratio X varies from 0.003 to0.3 in a capacitive load drive circuit having five stages, which isdifferent from the capacitive load drive circuit 301 having four stagesof FIG. 30 only in the number of stages. Note that, when the loadcapacitance ratio X is 0.003 to 0.03 (which is not shown in FIG. 91),the slew rate (10% to 90%) SR changes approximately in the same manneras in the case where the load capacitance ratio X is 0.001.

[0554] Further, FIG. 92 shows how the slew rate (10% to 90%) SR changeswith respect to the ratio x=Ts/τ0 of the time constant τ0 to theswitching time Ts when the load capacitance ratio X varies from 0.003 to0.3 in a capacitive load drive circuit having six stages, which isdifferent from the capacitive load drive circuit 301 having four stagesof FIG. 30 only in the number of stages. Note that, when the loadcapacitance ratio X is 0.003 to 0.1 (which is not shown in FIG. 92), theslew rate (10% to 90%) SR changes approximately in the same manner as inthe case where the load capacitance ratio X is 0.001.

[0555] The foregoing results revealed that a limit value of the slewrate (10% to 90%) SR is given by the following expressions:

[0556] when N=2(two stages),

SR=V/(R·Cd)*(−0.0002y ⁴+0.001y ³+0.009y ²−0.100y+0.386);

[0557] when N=3 (three stages),

SR=V/(R·Cd)*(0.0008y ⁴−0.012y ³+0.071y ²−0.229y +0.414);

[0558] when N=4(four stages),

SR=V/(R·Cd)*(0.0023y ⁴−0.028y ³+0.138y ²−0.336y+0.434); and

[0559] when N≧5(five or more stages),

SR=V/(R·Cd)*(0.0026y ⁴−0.032y ³+0.153y ²−0.356y+0.413),

[0560] where N is the number of times each condenser repeats the step ofcharging within one cycle of the drive pulse (number of stages).Accordingly, the switching time and the number of stages can be set withreference to the above expressions, when designing the slew rate.

[0561] Accordingly, circuit parameters and the switching time shouldsatisfy the following expressions, in order to satisfy the slew rate SRrequired for the apparatus:

[0562] when N=2(two stages),

SR<V/(R·Cd)*(−0.0002y ⁴+0.001y ³+0.009y ²−0.100y+0.386);

[0563] when N=3(three stages),

SR<V/(R·Cd)*(0.0008y ⁴−0.012y ³+0.071y ²−0.229y+0.414);

[0564] when N=4(four stages),

SR<V/(R·Cd)*(0.0023y ⁴−0.028y ³+0.138y ²−0.336y+0.434); and

[0565] when N>5(five or more stages),

SR<V/(R·Cd)*(0.0026y ⁴−0.032y ³+0.153y ²−0.356y+0.413).

[0566] Further, the apparatus that requires a high slew rate more than50(V/μsec), such as the apparatus employing an ink-jet method, shouldsatisfy the following conditions:

[0567] when N=2(two stages),

50(V/μsec)≦V/(R·Cd)*(−0.0002y ⁴+0.001y ³+0.009y ²−0.100y+0.386);

[0568] when N=3(three stages),

50(V/μsec)≦V/(R·Cd)*(0.0008y ⁴−0.012y ³+0.071y ²−0.229y+0.414);

[0569] when N=4(four stages),

50(V/μsec)≦V/(R·Cd)*(0.0023y ⁴−0.028y ³+0.138y ²−0.336y+0.434); and

[0570] when N≧5(five or more stages),

50(V/μsec)<V/(R·Cd)*(0.0026y ⁴−0.032y ³+0.153y ²−0.356y+0.413).

[0571] Further, the results shown in FIGS. 88 through 92 show that theslew rate of the waveform decreases as the number of stages in thecircuit increases.

[0572] [Embodiment 14]

[0573] Next, the following will explain yet another embodiment of thepresent invention with reference to FIGS. 38 and 39. Note that, forconvenience, members having the same functions as those used inforegoing Embodiments will be given the same reference symbols, andexplanation thereof will be omitted here.

[0574] As shown in FIG. 38, a capacitive load drive circuit 303 of thepresent embodiment has the same arrangement as the capacitive load drivecircuit 302 of Embodiment 13 except that a second electrical powersource (reference power source, reference potential terminal, and DCpower source) 319 having the same polarity as the electrical powersource 309, and a condenser C(0) are provided instead of the groundterminal C(0). In other words, the capacitive load drive circuit 303 ofthe present embodiment is provided with the first electrical powersource 309 and the second electrical power source 319 which have thesame polarity with each other, and generates a pulse of a voltagebetween the potential VH1 of the first electrical power source VH1 andthe potential VH2 of the second electrical power source VH2. Here, theabsolute value of the potential VH 1 of the first electrical powersource 309 is larger than the absolute value of the potential VH2 of thesecond electrical power source 319. Here, a circuit to supply initialelectric charge is omitted in the drawing.

[0575] With this arrangement, the capacitive load drive circuit carriesout the operation as shown in FIGS. 35(a) through 35(f), as inEmbodiment 13. Thus, by making (A) the electric charge flowing out ofthe condenser C(I) between FIGS. 35(a) and 35(b) to be approximatelyequal to (B) the electric charge flowing into the condenser C(I) betweenFIGS. 35(d) and 35(e), the condenser C(I) does not apparently consumeenergy during the cycle of FIGS. 35(a) through 35(f).

[0576] When generating a pulse, energy is consumed in such a manner thatthe electric charge which moves from the condenser C(N) to the condenserC(N−1) is transferred toward the second electrical power source 319 soas to be consumed at the second electrical power source 319.

[0577] Note that, the absolute value of the potential VH1 of the firstelectrical power source 309 may be smaller than the absolute value ofthe potential VH2 of the second electrical power source 319. In thiscase, when generating a pulse, energy is consumed in such a conversemanner that the electric charge which moves from the condenser C(0) tothe condenser C(1) is transferred toward the first electrical powersource 309 so as to be consumed at the first electrical power source309.

[0578] Further, the capacitive load drive circuit can operate withoutthe condenser C(N) which is connected to the first electrical powersource 309 or the condenser C(0) which is connected to the secondelectrical power source 319 (the condenser is generally integrated inthe electrical power source).

[0579] In this case, the first electrical power source 309 and thesecond electrical power source 319 can generate a pulse having apositive polarity as shown in FIG. 39, for example, when the firstelectrical power source 309 and the second electrical power source 319are positively-polarized power sources. Further, the first electricalpower source 309 and the second electrical power source 319 can generatea pulse having a negative polarity, which is obtained by reversing thepolarity of the pulse having the positive polarity as shown in FIG. 39,for example, when the first electrical power source 309 and the secondelectrical power source 319 are positively-polarized power sources.

[0580] [Embodiment 15]

[0581] Next, the following will explain still another embodiment of thepresent invention with reference to FIGS. 40 and 41. Note that, forconvenience, members having the same functions as those used inforegoing Embodiments will be given the same reference symbols, andexplanation thereof will be omitted here.

[0582] As shown in FIG. 40, a capacitive load drive circuit 304 of thepresent embodiment has the same arrangement as the capacitive load drivecircuit 302 of Embodiment 13 except that a second electrical powersource (reference power source, reference potential terminal) 319 whosepolarity is reverse to the electrical power source 309, and a condenserC(0) are provided instead of the ground terminal C(0). In other words,the capacitive load drive circuit 304 of the present embodiment isprovided with the first electrical power source (power source orreference power source) 309 and the second electrical power source(reference power source or power source) 329, which are power sourceshaving opposite polarities from each other; and generates a pulse of avoltage between the potential VH1 of the first electrical power sourceVH1 and the potential VH2 of the second electrical power source VH2. Inthis case, the potential of the first electrical power source 309 has apositive (+) polarity, and the potential of the second electrical powersource 329 has a negative (−) polarity. Here, a circuit to supplyinitial electric charge is omitted in the drawing.

[0583] The capacitive load drive circuit 304 of the present embodimentalso carries out the operation as shown in FIGS. 35(a) through 35(f), asin Embodiment 13. Thus, by making (A) the electric charge flowing out ofthe condenser C(I) between FIGS. 35(a) and 35(b) to be approximatelyequal to (B) the electric charge flowing into the condenser C(I) betweenFIGS. 35(d) and 35(e), the condenser C(I) does not apparently consumeenergy during the cycle of FIGS. 35(a) through 35(f).

[0584] When generating a positive pulse, energy is consumed in such amanner that the electric charge which moves from the condenser C(N) tothe condenser C(N−1) is transferred toward the second electrical powersource 329 so as to be consumed at a positively-charged condenser thathas a potential closest to the ground potential. On the other hand, whengenerating a negative pulse, energy is consumed in such a manner thatthe electric charge which moves from the condenser C(0) to the condenserC(1) is transferred toward the first electrical power source 309 so asto be consumed at a negatively-charged condenser that has a potentialclosest to the ground potential. When the first electrical power source309 and the second electrical power source 329 have the same absolutevalue, in particular, power consumed at the condenser having thepotential closest to the ground potential of the positive energy andpower consumed at the condenser having the potential closest to theground potential of the negative energy are canceled out, therebyeliminating the need for an external circuit to consume electricalpower.

[0585] The capacitive load drive circuit 304 of the present embodimentcan generate a pulse having a substantially sinusoidal waveform, asshown in FIG. 41, for example,

[0586] [Embodiment 16]

[0587] A capacitive load drive circuit of the present embodiment isarranged so that (A) the capacitive load drive circuit 302 of Embodiment13 for generating a positive pulse, which includes apositively-polarized electrical power source 309P (power supplypotential VH1), and (B) the capacitive load drive circuit 303 ofEmbodiment 14 for generating a negative pulse, which includes a secondnegatively-polarized electrical power source 319 (power supply potentialVH2) and a first electrical power source 309M (power supply potentialVH3), are connected in parallel. Here, a circuit to supply initialelectric charge is omitted in the drawing.

[0588] Here, when a condenser C(I−1)− of the capacitive load drivecircuit 303 has an initial potential of V(I−1)−, a condenser C(I)− ofthe capacitive load drive circuit 303 has an initial potential of V(I)−,a condenser C(I+1)− of the capacitive load drive circuit 303 has aninitial potential of V(I+1)−, a condenser C(I−1)+ of the capacitive loaddrive circuit 302 has an initial potential of V(I−1)+, a condenser C(I)+of the capacitive load drive circuit 302 has an initial potential ofV(I)+, and a condenser C(I+1)+ of the capacitive load drive circuit 302has an initial potential of V(I+1)+, the following relationships areobtained.

VH3< . . . <V(I−1)−<V(I)−<V(I+1)− . . . <VH2<0

0< . . . <V(I−1)+<V(I)+<V(I−1)+< . . . <VH1

[0589] In this case, it is possible to generate a pulse as shown in FIG.43, for example.

[0590] [Embodiment 17]

[0591] A capacitive load drive circuit of the present embodiment isarranged so that (A) the capacitive load drive circuit 303 of Embodiment14 for generating a positive pulse, the capacitive load drive circuit303 including the positively-polarized first electrical power source309P (power supply potential VH1) and the second electrical power supplysource 319 (power supply potential VH2), and (B) the capacitive loaddrive circuit 304 of Embodiment 15 for generating a negative pulse, thecapacitive load drive circuit 304 including the negatively-polarizedfirst electrical power source 309M (power supply potential VH3) areconnected in parallel, as shown in FIG. 44. The electrical power source319 (power supply potential VH2) is also used as the second electricalpower source 329 in the capacitive load drive circuit 304. Here, acircuit to supply initial electric charge to each condenser is omittedin the drawing.

[0592] Here, when a condenser C(I−1)− of the capacitive load drivecircuit 303 has an initial potential of V(I−1)−, a condenser C(I)− ofthe capacitive load drive circuit 303 has an initial potential of V(I)−,a condenser C(I+1)− of the capacitive load drive circuit 303 has aninitial potential of V(I+1)−, a condenser C(I-1)+ of the capacitive loaddrive circuit 304 has an initial potential of V(I-1)+, a condenser C(I)+of the capacitive load drive circuit 304 has an initial potential ofV(I)+, and a condenser C(I+1)+ of the capacitive load drive circuit 304has an initial potential of V(I+1)+, the following relationships areobtained.

VH3< . . . <V(I−1)−<V(I)−<V(I+1)− . . . <0

0<VH2<V(0)+< . . . <V(I−1)+<V(I)+<V(I−1)+< . . . <VH1

[0593] The electrical power source 319 is provided at a stage closest tothe ground potential, and has the function of absorbing electrical powerso as to prevent the voltage drift. The power supply potential VH2 ofthe electrical power source 319 may be set depending on how the initialpotentials of the condensers are set. In this case, it is possible togenerate a pulse as shown in FIG. 45, for example.

[0594] [Embodiment 18]

[0595] The capacitive load drive circuit of the present inventionsupplies to the capacitive load the electrostatic energy which isaccumulated in the plurality of energy accumulating elements, so as tocharge the capacitive load; and then collects the energy discharged fromthe capacitive load into the energy accumulating elements, so as toregenerate the electrostatic energy accumulated in the energyaccumulating elements to have a potential approximately equal to thepotential before the electrostatic energy is supplied to the capacitiveload. However, since the energy is regenerated only for a limited time,the energy accumulating elements do not completely regain the originalpotential. Thus, when charging and discharging are repeated withoutfurther energy supply after an initial potential is applied, the voltageof each energy accumulating element drifts (phenomenon in which thevoltage approaches an intermediate value between the highest potentialand the lowest potential), as shown in FIG. 68. Namely, an energyaccumulating element having an initial potential higher than theintermediate value between the highest potential and the lowestpotential insufficiently collects energy from the capacitive load,resulting in a gradual falling of the potential. On the other hand, anenergy accumulating element having an initial potential lower than theintermediate value between the highest potential and the lowestpotential excessively collects energy from the capacitive load,resulting in a gradual rising of the potential.

[0596] Note that, FIG. 68 is a view showing how the voltages of thecondensers C(1) through C(5) change in a capacitive load drive circuithaving the condensers C(1) through C(5), which is the capacitive loaddrive circuit 301 of FIG. 30 whose number of stages is modified intosix, in a case where the capacitive load 311 repeats charging anddischarging without further energy supply after initial potentials areapplied to the condensers C(1) through C(5), the initial potentialsbeing prepared by dividing the power supply voltage into six.

[0597] Thus, the capacitive load drive circuit 302 of Embodiment 13 isfurther provided with electrical power sources 339(1) through 339(N−1)(DC power sources) corresponding to the condensers C(1) through C(N−1)other than the ground terminal C(0) and the condenser C(N) that isconnected to the electrical power source 309, the electrical powersources 339(1) through 339(N−1) connecting to the condensers C(1)through C(N−1) via resistance circuits R(1) through R(N−1) so as tosupply energy, thereby preventing the above-described voltage drift.

[0598] As shown in FIG. 47, the capacitive load drive circuit 302 ofEmbodiment 13 may be additionally provided with the electrical powersources 339(1) through 339(N−1) which are respectively connected to thecondensers C(1) through C(N−1), and the resistors R(1) through R(N−1)which are respectively attached to the electrical power sources 339(1)through 339(N−1). Alternatively, as shown in FIG. 46, the capacitiveload drive circuit 303 of Embodiment 14 may be additionally providedwith the electrical power sources 339(1) through 339(N−1) which arerespectively connected to the condensers C(1) through C(N−1), and theresistors R(1) through R(N−1) which are respectively connected to theelectrical power sources 339(1) through 339(N−1). With this arrangementof FIG. 47, it is possible to generate a pulse as shown in FIG. 48, forexample.

[0599] Here, the resistors R(1) through R(N−1) which are respectivelyprovided between the electrical power sources 339(1) through 339(N−1)and the condensers C(1) through C(N−1) are preferably arranged so that atime constant that is determined by the resistors R(1) through R(N−1)and the capacitive component of the condensers C(1) through C(N−1) islarger than the cycle of a drive pulse applied to the capacitive load311, by not less than 50 times.

[0600] Namely, when the cycle of a drive pulse applied to the capacitiveload 311 (see FIG. 48) is a pulse generating cycle Tp, the capacitanceof the condenser C(I) (i=1, . . . I−1, I, I+1, . . . , N−1) is C(i), andthe resistance value of the resistance R(i) provided between theelectrical power source 339 and the condenser C(I) is R(i), the timeconstant τ(i) of the condenser C(i) is given as follows.

τ(i)=C(i)×R(i)

[0601] Here, it is preferable that the time constant τ(i) satisfies thefollowing relation.

Tp*10≦τ(i)=C(i)×R(i)

[0602] Further, it is more preferable that the time constant τ(i)satisfies the following relation.

Tp×50≦τ(i)=C(i)×R(i)

[0603] The following will explain the reasons for the above preferableranges.

[0604] When the electrical power sources 339(1) through 339(N−1) supplyelectrical power at excessively high speed, the electrical power sources339(1) through 339(N−1) supply electrical power to the condensers C(1)through C(N−1) before electrical power is regenerated by the circuit ofthe present invention, thereby deteriorating the efficiency inregenerating electrical power in the whole system.

[0605] The time constant of supplying electrical power from theelectrical power sources 339(1) through 339(N−1) should be larger thanthe time interval between energy is supplied to and regenerated from thecapacitive load 311, by not less than 20 times, in order that not morethan 5% of the electrical power is supplied from the electrical powersources 339(1) through 339(N−1) during a time interval between energy issupplied to and regenerated from the capacitive load 311. Further, thetime constant of supplying electrical power from the electrical powersources 339(1) through 339(N−1) should be larger than the time intervalbetween energy is supplied to and regenerated from the capacitive load311, by not less than 100 times, in order that not more than 1% of theelectrical power is supplied from the electrical power sources 339(1)through 339(N−1) during a time interval between energy is supplied toand regenerated from the capacitive load 311.

[0606] On the other hand, the longest time interval between supplyingand regenerating energy is considered to be a half of the pulsegenerating cycle Tp. Thus, the time constant τ(i) of supplyingelectrical power from the electrical power source 339(1) through339(N−1) should be larger than the pulse generating cycle Tp by not lessthan 10 times so that the electrical power supplied from the electricalpower sources 339(1) through 339(N−1) during a time interval betweenenergy is supplied to and regenerated from the capacitive load 311 isreduced to be not more than 5%. The time constant τ(i) of supplyingelectrical power from the electrical power sources 339(1) through339(N−1) should be not less than 50 times the pulse generating cycle Tpso that the electrical power supplied from the electrical power sources339(1) through 339(N−1) during a time interval between energy issupplied to and regenerated from the capacitive load 311 is reduced tobe not more than 1%. With this, the electrical power supplied from theelectrical power sources 339(1) through 339(N−1) do not substantiallyaffect the power regeneration.

[0607] There is no clear limitation on the upper limit of τ(i)/Tp, butthe electrical power sources 339(1) through 339(N−1) do not supplyenergy when τ(i)/Tp is too large. With this, the system cannot bestabilized when some reason causes the imbalance between energy supplyand regeneration. Namely, the time constant τ(i) of energy supply fromthe electrical power sources 339(1) through 339(N−1) is preferably assmall as possible within a range that does not significantly affect theenergy regeneration ratio.

[0608] The following will further explain this point.

[0609] As described above, the capacitive load drive circuit of thepresent embodiment for selectively connecting a plurality of condensersC(1) through C(N−1) so as to control a voltage applied to the capacitiveload 311 is so arranged that the electrical power sources 339(1) through339(N−1) supply energy to the condensers C(1) through C(N−1) so as toprevent the voltage drift caused by the fact that the condensers C(1)through C(N−1) charge and discharge the capacitive load 311.

[0610] Here, it is preferable that the capacitive load drive circuit isso arranged that a drive pulse having a predetermined cycle is appliedto the capacitive load 311, a charging step of selectively connectingthe capacitive load 311 to the condensers C(1) through C(N) so that thecondensers C(1) through C(N) supply electrostatic energy to thecapacitive load 311, the charging step being repeated in a plurality oftimes within one cycle of the drive pulse, and the followingrelationship is satisfied:

when N=2, 3×Tp≦Rs·Cs≦6×Tp;

when N=3, 3×Tp≦Rs·Cs≦7×Tp;

when N=4, 3×Tp≦Rs·Cs≦8×Tp;

when N≧5, 3×Tp≦Rs·Cs≦10×Tp,

[0611] where Cs (unit F) is the capacitive component of the condensersC(1) through C(N−1), Tp (unit Sec) is a cycle of the drive pulse appliedto the capacitive load 311, Rs is a resistance value of the energysupplying path from the electrical power sources 339(1) through 339(N−1)to the condensers C(1) through C(N−1) (first energy accumulatingelements), and N is the number of repeating the charging steps withinone cycle of the drive pulse (number of stages).

[0612] The following effects can be obtained by satisfying the aboverelational expressions. Namely, when the above relationship issatisfied, it is possible to maintain the voltages of the condensersC(1) through C(N−1), without affecting the power collection whencharging and discharging the capacitive load 311 which is acharacteristic feature of the present invention. In contrast, when Rs·Csis smaller than the above lower limit, the condensers C(1) throughC(N−1) are supplied with energy from the electrical power sources 339(1)through 339(N−1) before electrical power is sufficiently regenerated,thereby deteriorating the efficiency in regenerating electrical power.On the other hand, when Rs·Cs is extremely larger than the above lowerlimit, the voltage drift of the condensers C(1) through C(N−1) becomelarge, thereby deteriorating the efficiency in regenerating electricalpower. The upper limit of Rs·Cs differs depending on the energyconsumption in the capacitive load 311. In view of designing, Rs·Cs ispreferably as small as possible provided that the above relationship issatisfied.

[0613] Next, FIG. 49 shows an example of a capacitive load drive circuitof the present embodiment, which is designed to satisfy the aboverelationship. In this example, the number of stages (=N−1) of thecondensers C(1) through C(N−1), which are respectively connected to theelectrical power sources 339(1) through C(N−1) for preventing thevoltage drift, is modified to three (N=4) in the capacitive load drivecircuit of FIG. 46. Further, an equivalent ON resistor of the switchingelement S(N) is referred to as R here.

[0614] Further, it is assumed here that the capacitance (equivalentcapacitance of an ink jetting-out element (PZT) of an ink-jet printer)Cd of the capacitive load 311 is 1nF, the capacitances C(1) through C(3)of the condensers C(1) through C(3) are 10 nF (set to be 10 times asCd), the equivalent ON resistor R of the switching element S(N) is 10 Ω,the power supply voltage VH of the electrical power source 309 is 10V,the power supply voltage V(3) of the electrical power source 339(3) is7.5V, the power supply voltage V(2) of the electrical power source339(2) is 5.0 V, the power supply voltage V(1) of the electrical powersource 339(1) is 2.5 V, the pulse generating cycle Tp is 1 msec, and

R(1)=R(2)=R(3)=400 kΩ.

[0615] Accordingly, the time constant of charging and discharging thecapacitive load 311 is expressed as follows.

R×Cd=10 mSec

[0616] This is sufficiently shorter than the pulse generating cycle Tp.In this case, the right side of the relational expression Rs·Cs≦8×Tpwhen the number of stages is four is as follows:

8×Tp=8 mSec.

[0617] The left side of the relational expression Rs·Cs≦8×Tp when thenumber of stages is four is as follows:

Cs×Rs=400 kΩ×10 nF=4 mSec.

[0618] Accordingly, the relational expression Rs·Cs≦8×Tp when the numberof stages is four is expressed as follows:

4 mSec≦8 mSec,

[0619] which is now satisfied. Thus, in this case, energy supply fromthe electrical power sources can prevent the voltage drift of the energyaccumulating element Cs due to the application of a voltage pulse to thecapacitive load 311. Further, the examination of the relationalexpression 3×Tp≦Rs·Cs revealed that it is possible to reduce the voltagedrift in the exponential manner to be not more than 5%, by satisfyingthe relational expression, namely by setting the time constant to bethree or more times the pulse cycle. Therefore, it is necessary that therelational expression be satisfied to fully improve the stability andregeneration efficiency of the circuit.

[0620] [Embodiment 19]

[0621] A matrix display apparatus is provided with a display elementarray (display element) 340, a column selecting drive circuit 341, a rowselecting drive circuit 342, and an electrical power source 349 whichsupplies electrical power to the row selecting drive circuit 342.Selection with respect to the display element array 340 is carried outby the row selecting drive circuit (drive circuit) 342 and the columnselecting drive circuit (drive circuit) 341. A specified pulse isapplied to the display element array 340. The display element array hererefers to a liquid crystal display element array, a discharge display(plasma display), an EL element array, and the like. Here, thecapacitive load drive circuit of the present invention is used as acolumn pulse generating circuit that supplies a column pulse to thecolumn selecting drive circuit 341, so as to generate the column pulseand collect electrical power from the display element array. FIG. 59shows the case where the capacitive load drive circuit 305 of Embodiment18 is used as the column pulse generating circuit (including anelectrical power regenerating circuit), but the arrangement of thecapacitive load drive circuit is not particularly limited.

[0622] Note that, when the row selecting drive circuit 342 requires apulse generating apparatus, the capacitive load drive circuit of thepresent invention may be used instead of the electrical power source349.

[0623] [Embodiment 20]

[0624]FIG. 60 shows an application example where the capacitive loaddrive circuit of the present invention is used as a DC-AC converterwhich generates an AC voltage from a single voltage which is suppliedfrom a DC power source.

[0625] As shown in FIG. 60, the DC-AC converter is provided with acapacitive load drive circuit 601 of the present invention, a reversevoltage generating circuit 602 which generates a voltage whose polarityis reverse to a polarity of the voltage from a DC power source (notshown), and a voltage doubling circuit (double voltage generatingcircuit) 603 which generates a plurality of voltages. The capacitiveload drive circuit 601 has a function to generate an AC voltage whilecollecting electrical power. The DC-AC converter is arranged bycombining the usual reverse voltage generating circuit 602 and voltagedoubling circuit 603.

[0626] The operation of the DC-AC converter shown in FIG. 60 will beexplained using symbols as described in FIG. 60.

[0627] (1) The voltage V is always applied to the terminal A. Further,the voltage V is applied to the condenser C2.

[0628] (2) Next, the switching elements S1, S3, S4, S5, S9, and S10 areswitched ON so as to charge the condensers C1, C4, C5, and C6 to thevoltage V.

[0629] (3) The switching elements S1, S3, S4, S5, S9, and S10 areswitched OFF and then the switching elements S2, S6, S7, S8, S11, andS12, are switched ON, so as to charge the condensers C3, C7, C8, and C9to the voltage V.

[0630] (4) The switching elements S2, S6, S7, S8, S11, and S12 areswitched OFF, and then the switching elements S14, S16, S17, and S19 areswitched ON. With this, the condensers C4, C5, C6, C7, C8, and C9 areall connected in series, so as to generate voltages of 3V, 2V, V, −V,−2V, and −3V. The ground terminal GND is located at their center.

[0631] (5) The switching elements S15, S13, S18, and S20 where thevoltages of 2V, 3V, −2V, and −3V are respectively generated are switchedON so that C10, C12, C11, and C13 respectively accumulate the voltagesof 2V, 3V, −2V, and −3V. With this, each of the voltages is taken out tothe outside.

[0632] In sum, the DC-AC converter generates voltages by (i) connectingthe condensers C4, C5, C6, C7, C8, and C9 in parallel with respect tothe terminal A having the voltage V, so as to charge the condensers C4,C5, C6, C7, C8, and C9 to the voltage V, and then (ii) reconnecting thecondensers C4, C5, C6, C7, C8, and C9 in series.

[0633] [Embodiment 21]

[0634] An ink-jet printer may use a record head of a shearing mode whichuses a known piezoelectric material such as ceramic (Tokukaisho63-247051, for example). The following will explain the arrangement andfunction of a record head which is used for an ink-jet printer of theshearing mode.

[0635]FIG. 61 is a plan view showing a part of the record head which isseen from a recording medium, and FIG. 62 is a longitudinalcross-sectional view of the record head.

[0636] As shown in FIG. 61, a record head 1100 is provided with apiezoelectric material 200, a top plate 300, and a plurality of inkchambers 400.

[0637] The piezoelectric material 200 is formed in a comb-teeth shape,and each of the ink chambers 400 is inlaid into a gap between eachtooth.

[0638] The ink chamber 400 is provided with drive electrodes 500 whichare respectively formed on both side faces, and a jetting-out nozzle600. This ink-jet printer generates an electric field between the driveelectrodes 500 which are respectively provided in adjacent ink chambers400, so as to jet out ink through the jetting-out nozzle 600. Thedetails will be described later.

[0639] The top plate 300 inlays the plurality of ink chambers 400 intothe piezoelectric material 200, and is provided with connectingelectrodes made of conductive resin.

[0640] Further, as shown in FIG. 62, ink is stored in an ink tank 700 inthe record head 1100, and jetted out through the jetting-out nozzle in amanner to be described later via a common ink path 800 connected to thejetting-out nozzles 600 in the plurality of ink chambers 400.

[0641] Next, states how the ink-jet printer of the shearing mode jetsout ink will be explained. Note that, adjacent three ink chambers arerespectively referred to as A channel, B channel, and C channel in thefollowing explanation. Further, the following explanation will deal witha case where the ink chamber of the B channel jets out ink, but the sameapplies to cases where the ink chamber of the A channel or C channeljets out ink.

[0642] The record head 1100 is so arranged that the capacitive loaddrive circuits of Embodiments 5, 5A, 6, 6A drive the drive electrodes500 (capacitive load) in the ink chambers of the A channel, B channel,and C channel.

[0643] As shown in FIG. 63(a), in a normal state where ink is not jettedout, an electric field is not applied to any of the ink chambers of theA channel, B channel, and C channel. Further, the piezoelectric materialis polarized in a direction parallel to the surface of the driveelectrode, namely in a direction orthogonal to the drive electric field.

[0644] Then, as shown in FIG. 64, a jetting-out pulse is supplied to thedrive electrodes 500 in the ink chamber of the B channel. On the otherhand, a jetting-out pulse is not supplied to the ink chambers of the Achannel and B channel.

[0645] This generates an electric field from the drive electrodes 500 inthe ink chamber of the B channel respectively toward the driveelectrodes 500 in the ink chambers of the A channel and C channel. Thepiezoelectric material tries to move in accordance with the direction ofthis electric field. As a result, side walls of the ink chamber of the Bchannel expand, as shown in FIG. 63(a).

[0646] Then, as shown in FIG. 64, a common pulse is supplied to thedrive electrodes 500 in the ink chambers of the A channel and C channel.This generates an electric field from the drive electrodes 500 in theink chambers of the A channel and C channel respectively toward thedrive electrodes 500 in the ink chamber of the B channel. As a result,the side walls of the ink chamber of the B channel contract so as toreduce the volume of the ink chamber of the B channel, as shown in FIG.63(c). With this, ink is jetted out through the jetting-out nozzle ofthe ink chamber of the B channel.

[0647] Note that, when no channel jets out ink, a common pulse issupplied to the drive electrodes 500 in the ink chambers of the Achannel and C channel, and a non-jetting-out pulse which has the samepotential as the common pulse is supplied to the drive electrodes 500 inthe ink chamber of the B channel. With this, the drive electrodes 500 inthe ink chambers of the A through C channels have the same potential, soas to generate no electric field between each drive electrode 500.Accordingly, the side walls of the ink chambers of any channel do notexpand or contract. Here, ink is not jetted out.

[0648] As described above, the record head 1100 realizes printingoperation by repeating the sequential switching of the jetting-outchannels A through C so as to jet out ink, namely by three-phasedriving.

[0649] Further, a time AL for supplying the jetting-out pulse, and atime AL′ for supplying the common pulse are determined by the followingexpression (1).

AL (or AL′)=length of the ink chamber/speed of sound in ink  (1)

[0650] Therefore, when the ink chambers of the three channels have thesame length, the following relation is obtained.

AL′=2AL

[0651] Note that, in a typical ink-jet printer, obtained is about AL=2μs.

[0652] [Embodiment 22]

[0653] Next, the following will explain an embodiment of an ink-jetprinter which performs printing by jetting out ink onto a recordingmedium, and is improved in the jetting-out operation during therecovering operation, thereby being capable of carrying out printing inhigher definition and at higher speed than the ink-jet printer ofEmbodiment 21.

[0654] As shown in FIG. 65, an ink-jet printer 1001 is provided with apaper feeding section (paper feeding device) 1002, a separating section1003, a conveying section 1004, a printing section (character-printingsection) 1005, and a delivering-out section 1006.

[0655] The paper feeding section 1002 supplies a sheet P when printing,and is composed of a paper feeding tray 1007 and a pickup roller (notshown). When the printing is not carried out, the paper feeding section1002 stores the sheet P.

[0656] The separating section 1003 separately supplies to the printingsection 1005 a sheet P which is supplied from the paper feeding section1002. The separating section 1003 is provided with a paper feedingroller 1008 and a separating device 1009. The separating device 1009 isset so that friction between a pad portion thereof (portion contactingsheet) and sheet is more than friction between sheets. Further, thepaper feeding roller 1008 is set so that friction between the paperfeeding roller 1008 and sheet is more than the friction between the padand sheet, and the friction between sheets. Thus, even when two sheetsare sent to the separating section 1003, the paper feeding roller 1008can separate these two sheets so as to send only the upper sheet to theconveying section 1004.

[0657] The conveying section 1004 conveys to the printing section 1005the sheet P which is supplied one by one from the separating section1003. The conveying section 1004 is composed of a guide plate 1010 and apair of rollers 1011 (conveying mechanism). The pair of rollers 1011adjusts the conveying of the sheet P when conveying the sheet P into aspace between a record head 1100 and a platen 1013 so that ink from therecord head 1100 is sprayed on an appropriate portion of the sheet P.

[0658] The printing section 1005 prints on the sheet P which is suppliedfrom the pair of rollers 1011 of the conveying section 4. The printingsection 1005 is composed of the record head 1100 (print head), acarriage 1014 on which the record head 1 100 is mounted, a guide shaft1015 which guides the carriage 1014 (see FIG. 66), and the platen 1013which is a base plate for the sheet P upon printing.

[0659] The delivering-out section 1006 delivers the printed sheet P tothe outside of the ink-jet printer 1001, and is composed of an inkdrying section (not shown), a delivering-out roller 1016, and adelivering-out tray 1017.

[0660] With this arrangement, the ink-jet printer 1001 performs printingin such a manner as described below.

[0661] First, based on image information, a computer, etc. (not shown)sends request for printing to the ink-jet printer 1001. The ink-jetprinter 1001 which receives the request for printing carries the sheet Pon the paper feeding tray 1007 out of the paper feeding section 1002using the pick-up roller.

[0662] Next, the carried-out sheet P is passed through the separatingsection 1003 and sent to the conveying section 1004 by the paper feedingroller 1008. At the conveying section 1004, the pair of rollers 1011sends the sheet P into a space between the record head 1012 and theplaten 1013.

[0663] Then, at the printing section 1005, the jetting-out nozzle of therecord head 1012 sprays ink onto the sheet P on the platen 1013 inaccordance with image information. Here, the sheet P is temporallystopped on the platen 1013. While spraying ink, the carriage 1014 sweepsfor one line in a main scanning direction D2, guided by the guide shaft1015. Then, the sheet P is moved for a certain width on the platen 1013in a sub scanning direction D1. The printing section 1005 keeps carryingout this operation in accordance with image information. With this, theentire sheet P is subject to printing.

[0664] The printed sheet P passes through the ink drying section, and isdelivered to the delivering-out tray 1017 by the delivering-out roller1016. Then, the sheet P is supplied to a user as a printed product.

[0665] Next, the control system of the ink-jet printer 1001 of thepresent embodiment will be explained.

[0666] As shown in FIG. 67, a control section 1018 of the ink-jetprinter 1001 is provided with an interface section 1019, a memory 1020,an image processing section 1021, and a drive system control section1022.

[0667] The interface section 1019 is a circuit for exchanging signalsbetween (A) an external apparatus and (B) the image processing section1021 and the drive system control section 1022.

[0668] The image processing section 1021 performs image processing inaccordance with image information sent from the interface section 1019.Further, the image processing section 1021 is connected to a head drivecircuit 1023 which controls the driving of the record head 1100.

[0669] The drive system control section 1022 controls the driving of thecarriage 1014 and the conveying of the sheet P. More specifically, thedrive system control section 1022 is connected to a carriage drivecircuit 1024 which controls the driving of a carriage motor, and a paperconveying drive circuit 1025 which controls the driving of a paperconveying motor.

[0670] With this arrangement, the ink-jet printer drives the record head1100, the carriage 1014, the paper conveying motor, and the like, so asto perform the printing operation.

[0671] Next, the ink jetting-out operation of the record head 1100, inwhich the present embodiment is characterized, will be explained.

[0672] The record head 1100 is used for an ink-jet printer of theshearing mode which is provided with the piezoelectric material 200, thetop plate 300, the plurality of ink chambers 400, and the driveelectrodes 500.

[0673] In jetting-out operation for printing, the plurality of inkchambers 400 are three-phase driven in such a manner that three adjacentink chambers are separated into A channel, B channel, and C channel. Therecord head 1100 is so arranged that the drive electrodes 500(capacitive load) in the ink chambers of the A channel, B channel, and Cchannel are driven by the capacitive load drive circuits of Embodiment5, 5A, 6, and 6A. This is the three-phase driving which is explained indetail with reference to FIGS. 63 and 64, thus explanation thereof isomitted here.

[0674] As described above, a capacitive load drive circuit of thepresent invention is arranged so as to include a plurality of energyaccumulating elements for dividedly accumulating electrostatic energysupplied from a power source; and switching means for selectivelyconnecting the capacitive load and the plurality of energy accumulatingelements, (A) when charging the capacitive load, the switching meansselectively connecting the capacitive load and the plurality of energyaccumulating elements so that the plurality of energy accumulatingelements sequentially supply electrostatic energy to the capacitiveload, and (B) when discharging the capacitive load, the switching meansselectively connecting the capacitive load and the plurality of energyaccumulating elements so that the plurality of energy accumulatingelements sequentially collect electrostatic energy from the capacitiveload.

[0675] With this arrangement, the plurality of energy accumulatingelements sequentially supply electrostatic energy to the capacitive loadwhen charging, whereas the plurality of energy accumulating elementssequentially collect electrostatic energy from the capacitive load whendischarging. Accordingly, the system only consumes energy for an amountof uncollected electrostatic energy, thereby collecting and reusingenergy highly efficiently. Further, the above capacitive load drivecircuit is so arranged that the electrostatic energy accumulated in theenergy accumulating elements is directly collected, thereby onlyrequiring a simple circuit configuration. Therefore, the foregoingarrangement has a simple circuit configuration and is capable ofefficiently collecting and reusing energy accumulated in the capacitiveload so as to reduce electrical power consumption.

[0676] As described above, a capacitive load drive circuit of thepresent invention is arranged so as to include a plurality of energyaccumulating elements to which a plurality of different initialpotentials are respectively applied; a reference potential terminal towhich either a reference power supply potential from a power source or aground potential is applied as a reference potential; and switchingmeans for selectively connecting (A) the energy accumulating elementsand the reference potential terminal with (B) the capacitive load, oneof the plurality of energy accumulating elements being a first energyaccumulating element having a first initial potential which is not 0,one of the plurality of energy accumulating elements being a secondenergy accumulating element having a second initial potential whosepolarity is the same as a polarity of the first initial potential andwhose absolute value is larger than an absolute value of the firstinitial potential, the reference potential being either (a) the groundpotential, (a) a potential which has the same polarity as the firstinitial potential supplied from a reference power source and which has asmaller absolute value than the first initial potential, or (c) apotential whose polarity is reverse to the polarity of the first initialpotential supplied form the power source, the switching means carryingout (i) a first charging step of selectively connecting the capacitiveload with the reference potential terminal and then selectivelyconnecting the capacitive load with the first energy accumulatingelement so as to change, toward the first initial potential, a terminalvoltage of the capacitive load, (ii) a second charging step ofselectively connecting the capacitive load with the second energyaccumulating element so as to increase an absolute value of the terminalvoltage of the capacitive load, and (iii) a discharging step ofselectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the step (i), the steps (i) through (iii)being carried out in this order.

[0677] As described above, a capacitive load drive circuit of thepresent invention for charging and discharging a capacitive load isarranged so as to include a power supply terminal to which a powersupply potential from a power source is applied; a plurality of energyaccumulating elements to which a plurality of different initialpotentials are respectively applied; and switching means for selectivelyconnecting (A) the energy accumulating elements and the power supplyterminal with (B) the capacitive load, one of the plurality of energyaccumulating elements being a first energy accumulating element having afirst initial potential whose polarity is the same as a polarity of thepower supply potential and whose absolute value is smaller than anabsolute value of the power supply potential, one of the plurality ofenergy accumulating elements being a third energy accumulating elementhaving either (a) a potential whose polarity is the same as the polarityof the first initial potential and whose absolute value is smaller thanthe absolute value of the first initial potential, (a) a groundpotential, or (c) a third initial potential whose polarity is reverse tothe polarity of the first initial potential, the switching meanscarrying out (i) a first charging step of selectively connecting thecapacitive load with the third energy accumulating element and thenselectively connecting the capacitive load with the first energyaccumulating element so as to change, toward the first initialpotential, a terminal voltage of the capacitive load, (ii) a secondcharging step of selectively connecting the capacitive load with thepower supply terminal so as to increase an absolute value of theterminal voltage of the capacitive load, and (iii) a discharging step ofselectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the step (i), the steps (i) through (iii)being carried out in this order.

[0678] As described above, a capacitive load drive circuit of thepresent invention for charging and discharging a capacitive load isarranged so as to include a plurality of energy accumulating elements towhich a plurality of different initial potentials are respectivelyapplied; and switching means for selectively connecting the plurality ofenergy accumulating elements with the capacitive load, one of theplurality of energy accumulating elements being a first energyaccumulating element having a first initial potential which is not 0,one of the plurality of energy accumulating elements being a secondenergy accumulating element whose absolute value is larger than anabsolute value of the first initial potential, one of the plurality ofenergy accumulating elements being a third energy accumulating elementhaving either a potential whose polarity is the same as a polarity ofthe first initial potential and whose absolute value is smaller than theabsolute value of the first initial potential, a ground potential, or athird initial potential whose polarity is reverse to the polarity of thefirst initial potential, the switching means carrying out (i) a firstcharging step of selectively connecting the capacitive load with thethird energy accumulating element and then selectively connecting thecapacitive load with the first energy accumulating element so as tochange, toward the first initial potential, a terminal voltage of thecapacitive load, (ii) a second charging step of selectively connectingthe capacitive load with the second energy accumulating element so as toincrease an absolute value of the terminal voltage of the capacitiveload, and (iii) a discharging step of selectively connecting thecapacitive load with the first energy accumulating element so as todecrease the absolute value of the terminal voltage of the capacitiveload and so as to regenerate electrostatic energy to be accumulated inthe first energy accumulating element, the thus regeneratedelectrostatic energy being approximately equal to electrostatic energyas accumulated in the first energy accumulating element before the step(i), the steps (i) through (iii) being carried out in this order.

[0679] As described above, a capacitive load drive circuit of thepresent invention for charging and discharging a capacitive load isarranged so as to include a power supply terminal to which a powersupply potential from a power source is applied; a reference potentialterminal to which either a reference power supply potential that isdifferent from the power supply potential supplied from the power sourceor a ground potential is applied as a reference potential; a pluralityof first energy accumulating elements to which initial potentials arerespectively applied, the initial potentials being different from oneanother and being between the reference potential and the power supplypotential; and switching means for selectively connecting (A) thereference potential terminal, the plurality of energy accumulatingelements, and the power supply terminal with (B) the capacitive load,the switching means carrying out the steps of (1) connecting thecapacitive load with the reference potential terminal and thensequentially connecting the capacitive load with the first energyaccumulating elements in an order of the initial potentials from theinitial potential closest to the reference potential, so as to change,toward the power supply potential, a terminal voltage of the capacitiveload, (2) selectively connecting the capacitive load with the powersupply terminal so as to increase an absolute value of the terminalvoltage of the capacitive load, and (3) selectively connecting thecapacitive load with the first energy accumulating elements in an orderof the initial potentials from the initial potential closest to thepower supply potential, so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelements, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating elements before the step (1), the steps (1) through (3)being carried out in this order.

[0680] With these arrangements, when decreasing the absolute value ofthe terminal voltage of the capacitive load so as to discharge thecapacitive load, it is possible to regenerate electrostatic energyaccumulated in the first energy accumulating elements to beapproximately equal to electrostatic energy as accumulated in the firstenergy accumulating elements before supplying energy to the capacitiveload. Therefore, the first energy accumulating elements do notapparently consume energy, thereby regenerating electrical power highlyefficiently.

[0681] Further, it is preferable that each of the energy accumulatingelements is a condenser.

[0682] With this arrangement, by using the condenser which has a smallerinternal resistance than a secondary battery, etc., it is possible tocollect and reuse electrostatic energy highly efficiently. Further, byusing the condenser which is not much degraded even after repeatingcharging and discharging many times and thus has a long life, it ispossible to achieve a long-period use. Further, by using the condenserwhich has excellent frequency characteristics, it is possible to collectelectrostatic energy efficiently when driving a pulse of about 10 μm.

[0683] Further, the capacitive load drive circuit of the presentinvention may be arranged so as to further include an energy output pathwhich is connected to a part of the energy accumulating elements, theenergy output path supplying to an external element other than thecapacitive load the electrostatic energy that the energy accumulatingelement collects from the capacitive load.

[0684] With this arrangement, electrostatic energy collected to theenergy accumulating elements can be used by an external element otherthan the capacitive load from which the electrostatic energy iscollected, thereby efficiently reusing the electrostatic energycollected to the energy accumulating elements.

[0685] It is preferable that the plurality of energy accumulatingelements respectively have terminal voltages which are different fromone another; and (A) when charging the capacitive load, the switchingmeans sequentially connects the capacitive load with the energyaccumulating elements in an ascending order of absolute values of theterminal voltages and (B) when discharging the capacitive load, theswitching means sequentially connects the capacitive load with theenergy accumulating elements in a descending order of the absolutevalues of the terminal voltages.

[0686] With this arrangement, the energy accumulating elements areselectively connected sequentially in order of size of their terminalvoltages. Because of this, an inrush current supplied to the energyaccumulating elements and to the capacitive load is kept low, therebyreducing energy loss. As a result, it is possible to further reduceelectrical power consumption.

[0687] The capacitive load drive circuit of the present invention may beso arranged that when discharging the capacitive load, the switchingmeans grounds the capacitive load, after connecting the capacitive loadwith the energy accumulating element that has the terminal voltage of asmallest absolute value.

[0688] With this arrangement, the electric charge accumulated in theenergy accumulating elements is reduced to 0 before the energyaccumulating elements are charged, thereby achieving the stablerepeating operation of the energy accumulating elements.

[0689] The capacitive load drive circuit of the present invention may beso arranged that when discharging the capacitive load, the switchingmeans keeps connecting the capacitive load with the energy accumulatingelement that has the terminal voltage of a smallest absolute value untilthe capacitive load starts charging, after connecting the capacitiveload with the energy accumulating element that has the terminal voltageof the smallest absolute value.

[0690] With this arrangement, the energy accumulated in the capacitiveload can be retained and is not discarded, thereby collecting andreusing almost all of the electrostatic energy accumulated in thecapacitive load.

[0691] Further, the capacitive load drive circuit of the presentinvention may be arranged so as to further include voltage dividingmeans for dividing into a plurality of different voltages, the voltagesupplied from the power source and for supplying the divided voltagesrespectively to the energy accumulating elements.

[0692] With this arrangement, the voltage dividing means cancompulsorily adjust the terminal voltages of the energy accumulatingelements to predetermined voltages, even when the amount of electriccharge in the energy accumulating elements is not restored to an initialvalue (value before supplying electrostatic energy) after collectingelectrostatic energy from the capacitive load, due to the loss andenergy emission at the capacitive load, etc. As a result, it is possibleto supply a highly stable voltage to the capacitive load, therebyachieving stable repeating operation.

[0693] Further, with this arrangement, the plurality of energyaccumulating elements can sequentially supply different voltages to thecapacitive load so as to sequentially increase the drive voltage of thecapacitive load when charging the capacitive load, whereas the pluralityof energy accumulating elements sequentially supply different voltagesto the capacitive load so as to sequentially decrease the drive voltageof the capacitive load. Therefore, it is possible to obtain a variety ofwaveforms for the drive voltage by adjusting switching timings of theswitching means.

[0694] It is more preferable that the voltage dividing means equallydivides the voltage supplied from the power source into n (n is not lessthan 2). With this, it is possible to further reduce an inrush currentsupplied to the energy accumulating elements and to the capacitive load,thereby reducing energy loss.

[0695] The capacitive load drive circuit of the present invention may beso arranged that the voltage dividing means includes a plurality ofresistors which are connected in series with respect to the powersource. With this arrangement, it is possible to realize the voltagedividing means in a simple configuration.

[0696] The capacitive load drive circuit that employs the voltagedividing means including the plurality of resistors is preferablyarranged so as to further include buffer amplification means, which isprovided between (A) the resistors and (B) the energy accumulatingelements, for amplifying a current flowing through the resistors and foroutputting a voltage that differs from an input voltage so as to adjustto predetermined voltages, the terminal voltages of the energyaccumulating elements.

[0697] With this arrangement, the buffer amplification means canaccurately adjust the terminal voltages of the energy accumulatingelements to predetermined voltages, when the voltage divided by theresistors does not become exactly equal to the predetermined voltage,namely, for example, when the amount of electric charge in the energyaccumulating elements is not restored to an initial value (value beforesupplying electrostatic energy) after collecting electrostatic energyfrom the capacitive load, due to the loss and energy emission at thecapacitive load, etc. Further, with this arrangement, it is possible toreduce a current flowing through the resistors, thereby reducingelectrical power consumed by the resistors.

[0698] The capacitive load drive circuit of the present invention may beso arranged that the voltage dividing means includes a constant voltageelement such as a zener diode.

[0699] With this arrangement, the constant voltage element canaccurately adjust the terminal voltages of the energy accumulatingelements to predetermined voltages, even when the amount of electriccharge in the energy accumulating elements is not restored to an initialvalue (value before supplying electrostatic energy) after collectingelectrostatic energy from the capacitive load, due to the loss andenergy emission at the capacitive load, etc. As a result, it is possibleto supply a highly stable voltage to the capacitive load, therebyachieving stable repeating operation.

[0700] It is preferable that the voltage dividing means employing theconstant voltage element further includes a plurality of constantvoltage elements connected in series between the power source and aground line; and a resistor is inserted between (A) the constant voltageelements and (B) the power source or the ground line.

[0701] With this arrangement, even when the sum of set voltages of theconstant voltage elements is not equal to the power supply voltage, theresistor can absorb the difference in the voltages, thereby achievingstable repeating operation at a certain voltage.

[0702] The capacitive load drive circuit of the present invention may beso arranged that the voltage dividing means employing the constantvoltage element includes a first voltage divider and a second voltagedivider connected in parallel between the power source and a groundline; each of the first voltage divider and the second voltage dividerincludes the constant voltage means; a pull-up resistor is insertedbetween the constant voltage means and the power source in the firstvoltage divider; and a pull-down resistor is inserted between theconstant voltage means and the ground line in the second voltagedivider.

[0703] With this arrangement, even when the sum of set voltages of theconstant voltage elements is not equal to the power supply voltage, thepull-up resistor and the pull-down resistor can absorb the difference inthe voltages, thereby achieving stable repeating operation at a certainvoltage.

[0704] It is preferable that a difference between the number of constantvoltage elements included in the first voltage divider and the number ofconstant voltage elements included in the second voltage divider is notmore than one.

[0705] With this arrangement, it is possible to further improve thestability of the terminal voltages of the energy accumulating elements,thereby achieving stable repeating operation.

[0706] The capacitive load drive circuit of the present invention thatemploys the voltage dividing means including the constant voltageelement is preferably arranged so that a current-limit resistor which isinserted between the constant voltage means and the energy accumulatingelements.

[0707] With this arrangement, the current-limit resistor can absorb acurrent suddenly flowing in and out of the capacitive load, and canlimit a current flowing into the constant voltage elements, therebyreducing the workload of the constant voltage elements.

[0708] Further, it is preferable that all of the energy accumulatingelements respectively have one ends connected to the power source or theground line.

[0709] With this arrangement, the energy accumulating elements can berespectively separated so as not to interfere with one another. Thus,when a current from the capacitive load flows in and out of a particularenergy accumulating element, the voltage change of the particular energyaccumulating element does not affect the other energy accumulatingelements. Therefore, it is possible to further improve the stability ofthe terminal voltages of the energy accumulating elements, therebyachieving stable repeating operation.

[0710] Further, the capacitive load drive circuit of the presentinvention is preferably arranged so that a switching section forcontrolling the supply of electrostatic energy from the power source tothe energy accumulating elements, the switching section supplyingelectrostatic energy from the power source to the energy accumulatingelements only during a predetermined period before the capacitive loadis charged.

[0711] With this arrangement, the power source supplies electrostaticenergy to the energy accumulating elements only for a predetermineperiod. Thus, compared with a case where the power source alwayssupplies electrostatic energy to the energy accumulating elements, it ispossible to reduce electrical power consumed by the capacitive loaddrive circuit, and can particularly reduce electrical power consumed bythe resistors in the arrangement that employs the voltage dividing meansincluding the plurality of resistors connected in series with respect tothe power source.

[0712] Further, the capacitive load drive circuit of the presentinvention may be arranged so as to further include selecting means whichswitches over internal connecting states so as to selectively charge ordischarge one or some of capacitive loads.

[0713] With this arrangement, the selecting means selectively charge ordischarge one or some of the capacitive loads, thereby driving aplurality of capacitive loads at different timings.

[0714] Further, the capacitive load drive circuit that further employsthe selecting means is preferably arranged so that (A) an energysupplying path for supplying to the capacitive load the electrostaticenergy that is divided into the plurality of energy accumulatingelements and (B) an energy collecting path for collecting theelectrostatic energy from the plurality of energy accumulating elementsare separately provided; and each of the energy supplying path and theenergy collecting path includes the selecting means.

[0715] With this arrangement, by separately providing the energysupplying path (charge path) and the energy collecting path, it ispossible to simultaneously charge a part of the capacitive loads anddischarge the other part of the capacitive loads. With this, it ispossible to increase the number of operating the capacitive loads perunit time when driving many capacitive loads at different timings.Therefore, it is possible to operate the capacitive loads at a highspeed.

[0716] Further, the capacitive load drive circuit in which the energysupplying path and the energy collecting path are separately provided ispreferably arranged so as to further include rectifying means forrectifying currents of the energy supplying path and the energycollecting path.

[0717] With this arrangement, a short-circuit current does not flow in acase of delay in the ON/OFF operation of the switching means and thelike, thereby preventing the breakage of the circuit.

[0718] The capacitive load drive circuit can be applied to a piezoid forpressuring ink, the piezoid being provided in an ink-jet head that jetsout ink in droplets.

[0719] With this arrangement, it is possible to collect and reuse energyhighly efficiently when driving the piezoid of the ink-jet head whichgenerally consumes large electrical power, have a high dielectricconstant and a large capacitance, and is generally driven at a highrepeating frequency. This especially achieves the effect of reducingelectrical power consumption.

[0720] As described above, an ink-jet printer (image forming apparatus)of the present invention which includes an ink-jet head that uses apiezoid to pressurize ink so as to jet out the ink in droplets, and adrive circuit for driving the piezoid of the ink-jet head is so arrangedthat the drive circuit is one of the capacitive load drive circuits asarranged above.

[0721] With this arrangement, the plurality of energy accumulatingelements sequentially supply electrostatic energy to the piezoid, andthe plurality of energy accumulating elements sequentially collectelectrostatic energy from the piezoid, thereby collecting and reusingenergy highly efficiently. Therefore, it is possible to provide anink-jet printer (image forming apparatus) that has a lower electricalpower consumption.

[0722] As described above, a method for driving a capacitive load of thepresent invention is arranged so as to include an accumulating step ofdividedly accumulating electrostatic energy in a plurality of energyaccumulating elements; a charging step of sequentially supplying theelectrostatic energy from the plurality of energy accumulating elementsto the capacitive load so as to charge the capacitive load; and acollecting step of discharging the capacitive load so that the pluralityof energy accumulating elements sequentially collect the electrostaticenergy from the capacitive load.

[0723] With this method, the plurality of energy accumulating elementssequentially supply electrostatic energy to the piezoid, and theplurality of energy accumulating elements sequentially collectelectrostatic energy from the piezoid, thereby collecting and reusingenergy highly efficiently.

[0724] As described above, a method for driving a capacitive load of thepresent invention by charging and discharging the capacitive load isarranged so as to include (i) a step of preparing a first energyaccumulating element having an first initial potential which is not 0, asecond energy accumulating element, and a reference potential terminalto which either (a) a ground potential, (a) a potential which has thesame polarity as the first initial potential supplied from a powersource and which has a smaller absolute value than the first initialpotential, or (c) a potential whose polarity is reverse to the polarityof the first initial potential supplied form the power source is appliedas a reference potential; (ii) an initial potential applying step ofapplying the first initial potential to the first energy accumulatingelement, and applying to the second energy accumulating element a secondinitial potential which has the same polarity as the first initialpotential and which has a larger absolute value than the first initialpotential; (iii) a first charging step of selectively connecting thecapacitive load with the reference potential terminal and thenselectively connecting the capacitive load with the first energyaccumulating element so as to change, toward the first initialpotential, a terminal voltage of the capacitive load; (iv) a secondcharging step of selectively connecting the capacitive load with thesecond energy accumulating element so as to increase an absolute valueof the terminal voltage of the capacitive load; and (v) a dischargingstep of selectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the first charging step, the steps (iii)through (v) being carried out in this order.

[0725] As described above, a method for driving a capacitive load of thepresent invention by charging and discharging the capacitive load isarranged so as to include (i) a step of preparing a power supplyterminal to which a power supply potential is applied from a powersource, a first energy accumulating element, and a third energyaccumulating element; (ii) an initial potential applying step ofapplying to the first energy accumulating element a first initialpotential which has the same polarity as the power supply potential andwhich has a smaller absolute value than the power supply potential, andapplying to the third accumulating element either a potential which hasthe same polarity as the first initial potential and which has a smallerabsolute value than the first initial potential, a ground potential, ora third initial potential whose potential is reverse to the polarity ofthe first initial potential; (iii) a first charging step of selectivelyconnecting the capacitive load with the third energy accumulatingelement and then selectively connecting the capacitive load with thefirst energy accumulating element so as to change, toward the firstinitial potential, a terminal voltage of the capacitive load; (iv) asecond charging step of selectively connecting the capacitive load withthe power supply terminal so as to increase an absolute value of theterminal voltage of the capacitive load; and (v) a discharging step ofselectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the first charging step, the steps (iii)through (v) being carried out in this order.

[0726] As described above, a method for driving a capacitive load of thepresent invention by charging and discharging the capacitive load isarranged so as to include (i) a step of preparing a first energyaccumulating element, a second energy accumulating element, and a thirdenergy accumulating element; (ii) an initial potential applying step ofapplying to the first energy accumulating element a first initialpotential which is not 0, applying to the second energy accumulatingelement a second initial potential which has a larger absolute valuethan the initial potential of the first energy accumulating element, andapplying to the third accumulating element either a potential which hasthe same polarity as the first initial potential and which has a smallerabsolute value than the first initial potential, a ground potential, ora third initial potential whose potential is reverse to the polarity ofthe first initial potential; (iii) a first charging step of selectivelyconnecting the capacitive load with the third energy accumulatingelement and then selectively connecting the capacitive load with thefirst energy accumulating element so as to change, toward the firstinitial potential, a terminal voltage of the capacitive load; (iv) asecond charging step of selectively connecting the capacitive load withthe second energy accumulating element so as to increase an absolutevalue of the terminal voltage of the capacitive load; and (v) adischarging step of selectively connecting the capacitive load with thefirst energy accumulating element so as to decrease the absolute valueof the terminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the first charging step, the steps (iii)through (v) being carried out in this order.

[0727] As described above, a method for driving a capacitive load of thepresent invention by charging and discharging the capacitive load isarranged so as to include a providing step of preparing a power supplyterminal to which a power supply potential is applied from a powersource, a reference potential terminal to which either a reference powersupply potential supplied from the power source which is different fromthe power supply potential or a ground potential is applied as areference potential, and a plurality of first energy accumulatingelements; an initial potential applying step of respectively applying tothe plurality of first energy accumulating elements initial potentialswhich are different from one another and which are between the referencepotential and the power supply potential; and steps of (1) connectingthe capacitive load with the reference potential terminal and thensequentially connecting the capacitive load with the first energyaccumulating elements in an order of the initial potentials from theinitial potential closest to the reference potential, so as to change,toward the power supply potential, a terminal voltage of the capacitiveload, (2) selectively connecting the capacitive load with the powersupply terminal so as to increase an absolute value of the terminalvoltage of the capacitive load, and (3) selectively connecting thecapacitive load with the first energy accumulating elements in an orderof the initial potentials from the initial potential closest to thepower supply potential, so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelements, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating elements before the step (1), the steps (1) through (3)being carried out in this order.

[0728] With these methods, (A) the flow of energy from the energyaccumulating elements to the capacitive load when charging and (B) theflow of energy from the capacitive load to the energy accumulatingelements when discharging are canceled out, thereby reducing the energyloss. As a result, it is possible to reduce electrical powerconsumption.

[0729] As described above, an apparatus of the present invention is soarranged that the capacitive load drive circuit includes a power supplyterminal to which a power supply potential is applied from a powersource; a reference potential terminal to which either a reference powersupply potential supplied from the power source which is different fromthe power supply potential, or a ground potential is applied as areference potential; an energy accumulating element to which an initialpotential between the reference potential and the power supply potentialis applied; and switching means for selectively connecting (A) thereference potential terminal, the energy accumulating element, and thepower supply terminal with (B) the capacitive load, the switching meanscarrying out (i) a first charging step of connecting the capacitive loadwith the reference potential terminal and then connecting the capacitiveload with the energy accumulating element, (ii) a second charging stepof selectively connecting the capacitive load with the power supplyterminal, and (iii) a discharging step of connecting the capacitive loadwith the energy accumulating element, the steps (i) through (iii) beingcarried out in this order, the following relationship being satisfied:

Cd/Cs≦0.164{Ts/(R·Cd)}^(0.2198), if Ts/(R·Cd)<2.5;

[0730] and

Cd/Cs≦0.2, if Ts/(R·Cd)≧2.5,

[0731] where Cs is a capacitive component of the energy accumulatingelement, Cd is a capacitance of the capacitive load, Ts is a time duringwhich the energy accumulating element is kept connected to thecapacitive load, and R is a resistance value of charge and dischargepaths of the energy accumulating element with respect to the capacitiveload, the charge and discharge paths including switching means.

[0732] Further, as described above, an apparatus of the presentinvention is arranged so that the capacitive load drive circuit includesa power supply terminal to which a power supply potential is appliedfrom a power source; a reference potential terminal to which either areference power supply potential supplied from the power source which isdifferent from the power supply potential, or a ground potential isapplied as a reference potential; a plurality of energy accumulatingelements to which initial potentials are respectively applied, theinitial potentials being different from one another and being betweenthe reference potential and the power supply potential; and switchingmeans for selectively connecting (A) the reference potential terminal,the plurality of energy accumulating elements, and the power supplyterminal with (B) the capacitive load, the switching means carrying out(i) a first charging step of connecting the capacitive load with thereference potential terminal and then sequentially connecting thecapacitive load with the energy accumulating elements in an order of theinitial potentials from the initial potential closest to the referencepotential, (ii) a second charging step of selectively connecting thecapacitive load with the power supply terminal, and (iii) a dischargingstep of sequentially connecting the capacitive load with the energyaccumulating elements in an order of the initial potentials from theinitial potential closest to the power supply potential, the steps (i)through (iii) being carried out in this order, the followingrelationship being satisfied:

Cd/Cs≦0.164{Ts/(R·Cd)}^(0.2198), if Ts/(R·Cd)<2.5;

[0733] and

Cd/Cs≦0.2, if Ts/(R·Cd)≧2.5,

[0734] where Cs is a capacitive component of the energy accumulatingelements, Cd is a capacitance of the capacitive load, Ts is a timeduring which the energy accumulating elements are kept connected to thecapacitive load, and R is a resistance value of charge and dischargepaths of the energy accumulating elements with respect to the capacitiveload, the charge and discharge paths including switching means.

[0735] With these arrangements, when decreasing the absolute value ofthe terminal voltage of the capacitive load so as to discharge thecapacitive load, it is possible to regenerate electrostatic energyaccumulated in the first energy accumulating elements to beapproximately equal to electrostatic energy as accumulated in the firstenergy accumulating elements before supplying energy to the capacitiveload. Therefore, the first energy accumulating elements do notapparently consume energy, thereby regenerating electrical power highlyefficiently.

[0736] Further, with these arrangements, the voltage of the capacitiveload reaches 90% of the final attainment voltage (final voltage attainedby the capacitive load after repeating the first through third stepsinfinitely) during the first through third steps. With this, change inthe voltages of the energy accumulating elements due to the flowing ofelectric charge from the energy accumulating elements to the capacitiveload is reduced, and the electrical power regeneration ratio ingenerating pulses is improved, thereby further reducing the electricalpower consumption. Further, change in the voltages of the energyaccumulating elements due to the generation of a pulse is reduced. Thisallows to generate a next pulse without correcting the voltage change.

[0737] The invention being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

INDUSTRIAL APPLICABILITY

[0738] As describe above, the present invention can provide a capacitiveload drive circuit for driving a capacitive load which can reduceelectrical power consumption, a capacitive load driving method, and anapparatus using the same.

[0739] Therefore, the present invention can be preferably used for (A) acapacitive load drive circuit for driving a capacitive load, which isprovided in an image forming apparatus that uses a piezoid and anelectrostatic drive electrode to jet out ink, the piezoid and theelectrostatic drive electrode being capacitive loads, a dischargeelectrode of a plasma display, a drive circuit of a liquid crystaldisplay, or the like, (B) a capacitive load driving method, and (C) anapparatus using the same, such as an image forming apparatus, a displayapparatus, a voltage pulse generating apparatus, and a DC-AC converter.

1. A capacitive load drive circuit for charging and discharging acapacitive load, comprising: a plurality of energy accumulating elementsfor dividedly accumulating electrostatic energy supplied from a powersource; and switching means for selectively connecting the capacitiveload and the plurality of energy accumulating elements, (A) whencharging the capacitive load, the switching means selectively connectingthe capacitive load and the plurality of energy accumulating elements sothat the plurality of energy accumulating elements sequentially supplyelectrostatic energy to the capacitive load, and (B) when dischargingthe capacitive load, the switching means selectively connecting thecapacitive load and the plurality of energy accumulating elements sothat the plurality of energy accumulating elements sequentially collectelectrostatic energy from the capacitive load.
 2. A capacitive loaddrive circuit for charging and discharging a capacitive load,comprising: a plurality of energy accumulating elements to which aplurality of different initial potentials are respectively applied; areference potential terminal to which either a reference power supplypotential from a power source or a ground potential is applied as areference potential; and switching means for selectively connecting (A)the energy accumulating elements and the reference potential terminalwith (B) the capacitive load, one of the plurality of energyaccumulating elements being a first energy accumulating element having afirst initial potential which is not 0, one of the plurality of energyaccumulating elements being a second energy accumulating element havinga second initial potential whose polarity is the same as a polarity ofthe first initial potential and whose absolute value is larger than anabsolute value of the first initial potential, the reference potentialbeing either (a) the ground potential, (a) a potential which has thesame polarity as the first initial potential supplied from the powersource and which has a smaller absolute value than the first initialpotential, or (c) a potential whose polarity is reverse to the polarityof the first initial potential supplied form the power source, theswitching means carrying out (i) a first charging step of selectivelyconnecting the capacitive load with the reference potential terminal andthen selectively connecting the capacitive load with the first energyaccumulating element so as to change, toward the first initialpotential, a terminal voltage of the capacitive load, (ii) a secondcharging step of selectively connecting the capacitive load with thesecond energy accumulating element so as to increase an absolute valueof the terminal voltage of the capacitive load, and (iii) a dischargingstep of selectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the step (i), the steps (i) through (iii)being carried out in this order.
 3. The capacitive load drive circuit asset forth in claim 2, wherein: the reference potential terminal is aground terminal having the ground potential; the switching means is aplurality of switching elements, which are respectively provided between(A) the ground terminal and the plurality of energy accumulatingelements and (B) the capacitive load, for selectively connecting (A) theground terminal and the plurality of energy accumulating elements with(B) the capacitive load; and at least the accumulating element that hasan initial potential whose absolute value is largest among the pluralityof accumulating elements is directly or indirectly connected with thepower source.
 4. A capacitive load drive circuit for charging anddischarging a capacitive load, comprising: a power supply terminal towhich a power supply potential from a power source is applied; aplurality of energy accumulating elements to which a plurality ofdifferent initial potentials are respectively applied; and switchingmeans for selectively connecting (A) the energy accumulating elementsand the power supply terminal with (B) the capacitive load, one of theplurality of energy accumulating elements being a first energyaccumulating element having a first initial potential whose polarity isthe same as a polarity of the power supply potential and whose absolutevalue is smaller than an absolute value of the power supply potential,one of the plurality of energy accumulating elements being a thirdenergy accumulating element having either (a) a potential whose polarityis the same as the polarity of the first initial potential and whoseabsolute value is smaller than the absolute value of the first initialpotential, (b) a ground potential, or (c) a third initial potentialwhose polarity is reverse to the polarity of the first initialpotential, the switching means carrying out (i) a first charging step ofselectively connecting the capacitive load with the third energyaccumulating element and then selectively connecting the capacitive loadwith the first energy accumulating element so as to change, toward thefirst initial potential, a terminal voltage of the capacitive load, (ii)a second charging step of selectively connecting the capacitive loadwith the power supply terminal so as to increase an absolute value ofthe terminal voltage of the capacitive load, and (iii) a dischargingstep of selectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the step (i), the steps (i) through (iii)being carried out in this order.
 5. A capacitive load drive circuit forcharging and discharging a capacitive load, comprising: a plurality ofenergy accumulating elements to which a plurality of different initialpotentials are respectively applied; and switching means for selectivelyconnecting the plurality of energy accumulating elements with thecapacitive load, one of the plurality of energy accumulating elementsbeing a first energy accumulating element having a first initialpotential which is not 0, one of the plurality of energy accumulatingelements being a second energy accumulating element whose absolute valueis larger than an absolute value of the first initial potential, one ofthe plurality of energy accumulating elements being a third energyaccumulating element having either a potential whose polarity is thesame as a polarity of the first initial potential and whose absolutevalue is smaller than the absolute value of the first initial potential,a ground potential, or a third initial potential whose polarity isreverse to the polarity of the first initial potential, the switchingmeans carrying out (i) a first charging step of selectively connectingthe capacitive load with the third energy accumulating element and thenselectively connecting the capacitive load with the first energyaccumulating element so as to change, toward the first initialpotential, a terminal voltage of the capacitive load, (ii) a secondcharging step of selectively connecting the capacitive load with thesecond energy accumulating element so as to increase an absolute valueof the terminal voltage of the capacitive load, and (iii) a dischargingstep of selectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the step (i), the steps (i) through (iii)being carried out in this order.
 6. The capacitive load drive circuit asset forth in claim 5, further comprising: a ground terminal having theground potential, the switching means being a plurality of switchingelements, which are respectively provided between (A) the groundterminal and the plurality of energy accumulating elements and (B) thecapacitive load, for selectively connecting (A) the ground terminal andthe plurality of energy accumulating elements with (B) the capacitiveload, at least the accumulating element that has an initial potentialwhose absolute value is largest among the plurality of accumulatingelements being directly or indirectly connected with the power source.7. The capacitive load drive circuit as set forth in claim 5, wherein:the switching means is a plurality of switching elements, which arerespectively provided between the plurality of energy accumulatingelements and the capacitive load, for selectively connecting theplurality of energy accumulating elements with the capacitive load, atleast the accumulating element that has an initial potential whoseabsolute value is largest among the plurality of accumulating elementsis directly or indirectly connected with the power source.
 8. Acapacitive load drive circuit for charging and discharging a capacitiveload, comprising: a power supply terminal to which a power supplypotential from a power source is applied; a reference potential terminalto which either a reference power supply potential that is differentfrom the power supply potential or a ground potential is applied as areference potential; a plurality of first energy accumulating elementsto which initial potentials are respectively applied, the initialpotentials being different from one another and being between thereference potential and the power supply potential; and switching meansfor selectively connecting (A) the reference potential terminal, theplurality of energy accumulating elements, and the power supply terminalwith (B) the capacitive load, the switching means carrying out the stepsof (1) connecting the capacitive load with the reference potentialterminal and then sequentially connecting the capacitive load with thefirst energy accumulating elements in an order of the initial potentialsfrom the initial potential closest to the reference potential, so as tochange, toward the power supply potential, a terminal voltage of thecapacitive load, (2) selectively connecting the capacitive load with thepower supply terminal so as to increase an absolute value of theterminal voltage of the capacitive load, and (3) selectively connectingthe capacitive load with the first energy accumulating elements in anorder of the initial potentials from the initial potential closest tothe power supply potential, so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelements, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating elements before the step (1), the steps (1) through (3)being carried out in this order.
 9. The capacitive load drive circuit asset forth in any one of claims 2 through 8, further comprising: a DCpower source which is connected to the first energy accumulating elementvia a resistance circuit, the DC power source supplying energy into thefirst energy accumulating element so as to prevent a voltage drift ofthe first energy accumulating element caused by the charging anddischarging of the capacitive load.
 10. The capacitive load drivecircuit as set forth in claim 9, wherein: a drive pulse having apredetermined cycle is applied to the capacitive load; and a timeconstant determined by a resistance value of the resistance circuit anda capacitive component of the first energy accumulating element islarger than the cycle of the drive pulse applied to the capacitive load,by 50 times or more.
 11. The capacitive load drive circuit as set forthin claim 9, wherein: a drive pulse having a predetermined cycle isapplied to the capacitive load; the switching means carries out acharging step of selectively connecting the capacitive load to differentpoints so as to supply electrostatic energy to the capacitive load, thecharging step being repeated in a plurality of times within one cycle ofthe drive pulse; and the following relationship is satisfied:3×Tp≦Rs·Cs≦6×Tp, where N=2;3×Tp≦Rs·Cs≦7×Tp, where N=3;3×Tp≦Rs·Cs≦8×Tp,where N=4; and3×Tp≦Rs·Cs≦10×Tp, where N≧5, where Cs is a capacitivecomponent of the first energy accumulating element, Tp is the cycle ofthe drive pulse applied to the capacitive load, Rs is a resistance valueof an energy supplying path from the DC power source to the first energyaccumulating element, and N is the number of repeating the charging stepduring the cycle of the drive pulse.
 12. The capacitive load drivecircuit as set forth in any one of claims 1 through 11, wherein: each ofthe energy accumulating elements has an initial potential whose polarityis positive.
 13. The capacitive load drive circuit as set forth in anyone of claims 1 through 11, wherein: each of the energy accumulatingelements has an initial potential whose polarity is negative.
 14. Acapacitive load drive circuit, wherein: the capacitive load drivecircuit as set forth in claim 12 and the capacitive load drive circuitas set forth in claim 13 are connected in parallel.
 15. The capacitiveload drive circuit as set forth in any one of claims 1 through 14,wherein: the plurality of energy accumulating elements respectively haveterminal voltages which are different from one another; and (A) whencharging the capacitive load, the switching means sequentially connectsthe capacitive load with the energy accumulating elements in anascending order of absolute values of the terminal voltages and (B) whendischarging the capacitive load, the switching means sequentiallyconnects the capacitive load with the energy accumulating elements in adescending order of the absolute values of the terminal voltages. 16.The capacitive load drive circuit as set forth in any one of claims 1through 15, wherein: each of the energy accumulating elements is acondenser.
 17. The capacitive load drive circuit as set forth in any oneof claims 1 through 15, further comprising: an energy output path whichis connected to a part of the energy accumulating elements, the energyoutput path supplying to an external element other than the capacitiveload the electrostatic energy that the energy accumulating elementcollects from the capacitive load.
 18. The capacitive load drive circuitas set forth in claim 17, wherein: when discharging the capacitive load,the switching means grounds the capacitive load, after connecting thecapacitive load with the energy accumulating element that has theterminal voltage of a smallest absolute value.
 19. The capacitive loaddrive circuit as set forth in claim 16, wherein: when discharging thecapacitive load, the switching means keeps connecting the capacitiveload with the energy accumulating element that has the terminal voltageof a smallest absolute value until the capacitive load starts charging,after connecting the capacitive load with the energy accumulatingelement that has the terminal voltage of the smallest absolute value.20. The capacitive load drive circuit as set forth in any one of claims1 through 19, further comprising: voltage dividing means for dividinginto a plurality of different voltages, the voltage supplied from thepower source and for supplying the divided voltages respectively to theenergy accumulating elements.
 21. The capacitive load drive circuit asset forth in claim 20, further comprising: a switching section forcontrolling the supply of the voltages from the voltage dividing meansto the energy accumulating elements, the switching section beingswitched ON only during a predetermined period before the capacitiveload is charged.
 22. The capacitive load drive circuit as set forth inclaim 20, further comprising: a ground terminal; a DC power source forsupplying a power supply voltage; and voltage dividing means, which isconnected between the ground terminal and the DC power source, fordividing a potential difference between a ground potential and the powersupply voltage, the plurality of energy accumulating elements beingrespectively connected to voltage dividing points to which the voltagesthat are divided by the voltage dividing means are respectivelysupplied.
 23. The capacitive load drive circuit as set forth in claim20, further comprising: a plurality of DC power sources respectivelyhaving different power supply voltages; and voltage dividing means,which is connected between the DC power sources, for dividing apotential difference among the power supply voltages, the plurality ofenergy accumulating elements being respectively connected to voltagedividing points to which the voltages that are divided by the voltagedividing means are respectively supplied.
 24. The capacitive load drivecircuit as set forth in claim 20, wherein: the voltage dividing meansincludes a plurality of resistors which are connected in series withrespect to the power source.
 25. The capacitive load drive circuit asset forth in claim 20, further comprising: buffer amplification means,which is provided between (A) the resistors and (B) the energyaccumulating elements, for amplifying a current flowing through theresistors and for outputting a voltage that differs from an inputvoltage so as to adjust to predetermined voltages, the terminal voltagesof the energy accumulating elements.
 26. The capacitive load drivecircuit as set forth in claim 20, wherein: the voltage dividing meansincludes constant voltage means for stabilizing the divided voltages.27. The capacitive load drive circuit as set forth in claim 26, wherein:the voltage dividing means further includes a plurality of constantvoltage elements connected in series between the power source and aground line; and a resistor is inserted between (A) the constant voltageelements and (B) the power source or the ground line.
 28. The capacitiveload drive circuit as set forth in claim 26, wherein: the voltagedividing means includes a first voltage divider and a second voltagedivider connected in parallel between the power source and a groundline; each of the first voltage divider and the second voltage dividerincludes the constant voltage means; a pull-up resistor is insertedbetween the constant voltage means and the power source in the firstvoltage divider; and a pull-down resistor is inserted between theconstant voltage means and the ground line in the second voltagedivider.
 29. The capacitive load drive circuit as set forth in claim 28,wherein: a difference between the number of constant voltage elementsincluded in the first voltage divider and the number of constant voltageelements included in the second voltage divider is not more than one.30. The capacitive load drive circuit as set forth in any one of claims26 through 29, further comprising: a current-limit resistor which isinserted between the constant voltage means and the energy accumulatingelements.
 31. The capacitive load drive circuit as set forth in any oneof claims 26 through 30, wherein: the constant voltage means includes aconstant voltage element, the constant voltage element is a zener diode.32. The capacitive load drive circuit as set forth in any one of claims1 through 31, wherein: all of the energy accumulating elementsrespectively have one ends connected to the power source or the groundline.
 33. The capacitive load drive circuit as set forth in any one ofclaims 1 through 32, further comprising: a switching section forcontrolling the supply of electrostatic energy from the power source tothe energy accumulating elements, the switching section supplyingelectrostatic energy from the power source to the energy accumulatingelements only during a predetermined period before the capacitive loadis charged.
 34. The capacitive load drive circuit as set forth in anyone of claims 1 through 33, further comprising: selecting means whichswitches over internal connecting states so as to selectively charge ordischarge one or some of capacitive loads.
 35. The capacitive load drivecircuit as set forth in claim 34, wherein: (A) an energy supplying pathfor supplying to the capacitive load the electrostatic energy that isdivided into the plurality of energy accumulating elements and (B) anenergy collecting path for collecting the electrostatic energy from theplurality of energy accumulating elements are separately provided; andeach of the energy supplying path and the energy collecting pathincludes the selecting means.
 36. The capacitive load drive circuit asset forth in claim 35, further comprising: rectifying means forrectifying currents of the energy supplying path and the energycollecting path.
 37. The capacitive load drive circuit as set forth inany one of claims 1 through 36, wherein: the capacitive load is apiezoid for pressuring ink, the piezoid being provided in an ink-jethead that jets out ink in droplets.
 38. The capacitive load drivecircuit as set forth in any one of claims 1 through 36, wherein: thecapacitive load is an electrostatic drive electrode, which is providedin an ink-jet head of an electrostatic method that uses electrostaticattraction force to jet out ink in droplets.
 39. An apparatus whichincludes the capacitive load drive circuit as set forth in any one ofclaims 1 through 38, and the capacitive load that is charged anddischarged by the capacitive load drive circuit, wherein: the followingrelationship is satisfied: Cd/Cs≦0.164{Ts/(R·Cd)}^(0.2198), ifTs/(R·Cd)<2.5; and Cd/Cs≦0.2, if Ts/(R·Cd)≧2.5, where Cs is a capacitivecomponent of the energy accumulating elements, Cd is a capacitance ofthe capacitive load, Ts is a time during which the energy accumulatingelements are kept connected to the capacitive load, and R is aresistance value of charge and discharge paths of the energyaccumulating elements with respect to the capacitive load, the chargeand discharge paths including the switching means.
 40. An apparatuswhich includes the capacitive load drive circuit as set forth in any oneof claims 1 through 38, and the capacitive load that is charged anddischarged by the capacitive load drive circuit, wherein: the capacitivecomponent of the energy accumulating elements is larger than thecapacitance of the capacitive load, by 100 times or more.
 41. Anapparatus which includes a capacitive load, and a capacitive load drivecircuit for charging and discharging the capacitive load, wherein: thecapacitive load drive circuit includes: a power supply terminal to whicha power supply potential is applied from a power source; a referencepotential terminal to which either a reference power supply potentialsupplied from the power source which is different from the power supplypotential, or a ground potential is applied as a reference potential; anenergy accumulating element to which an initial potential between thereference potential and the power supply potential is applied; andswitching means for selectively connecting (A) the reference potentialterminal, the energy accumulating element, and the power supply terminalwith (B) the capacitive load, the switching means carrying out (i) afirst charging step of connecting the capacitive load with the referencepotential terminal and then connecting the capacitive load with theenergy accumulating element, (ii) a second charging step of selectivelyconnecting the capacitive load with the power supply terminal, and (iii)a discharging step of connecting the capacitive load with the energyaccumulating element, the steps (i) through (iii) being carried out inthis order, the following relationship being satisfied:Cd/Cs≦0.164{Ts/(R·Cd)}^(0.2198), if Ts/(R·Cd)<2.5; and Cd/Cs≦0.2, ifTs/(R·Cd)≧2.5, where Cs is a capacitive component of the energyaccumulating element, Cd is a capacitance of the capacitive load, Ts isa time during which the energy accumulating element is kept connected tothe capacitive load, and R is a resistance value of charge and dischargepaths of the energy accumulating element with respect to the capacitiveload, the charge and discharge paths including switching means.
 42. Anapparatus which includes a capacitive load, and a capacitive load drivecircuit for charging and discharging the capacitive load, wherein: thecapacitive load drive circuit includes: a power supply terminal to whicha power supply potential is applied from a power source; a referencepotential terminal to which either a reference power supply potentialsupplied from the power source which is different from the power supplypotential, or a ground potential is applied as a reference potential; aplurality of energy accumulating elements to which initial potentialsare respectively applied, the initial potentials being different fromone another and being between the reference potential and the powersupply potential; and switching means for selectively connecting (A) thereference potential terminal, the plurality of energy accumulatingelements, and the power supply terminal with (B) the capacitive load,the switching means carrying out (i) a first charging step of connectingthe capacitive load with the reference potential terminal and thensequentially connecting the capacitive load with the energy accumulatingelements in an order of the initial potentials from the initialpotential closest to the reference potential, (ii) a second chargingstep of selectively connecting the capacitive load with the power supplyterminal, and (iii) a discharging step of sequentially connecting thecapacitive load with the energy accumulating elements in an order of theinitial potentials from the initial potential closest to the powersupply potential, the steps (i) through (iii) being carried out in thisorder, the following relationship being satisfied:Cd/Cs≦0.164{Ts/(R·Cd)}^(0.2198), if Ts/(R·Cd)<2.5; and Cd/Cs≦0.2, ifTs/(R·Cd)≧2.5, where Cs is a capacitive component of the energyaccumulating elements, Cd is a capacitance of the capacitive load, Ts isa time during which the energy accumulating elements are kept connectedto the capacitive load, and R is a resistance value of charge anddischarge paths of the energy accumulating elements with respect to thecapacitive load, the charge and discharge paths including switchingmeans.
 43. The apparatus as set forth in claim 41, wherein the followingrelationship is satisfied: SR≦V/(R·Cd)*(−0.0002y ⁴+0.001y ³+0.009y²−0.100y+0.386),where Cd is the capacitance of the capacitive load, R isthe resistance value of the charge and discharge paths of the energyaccumulating element with respect to the capacitive load, the charge anddischarge paths including the switching means, Ts is the time duringwhich the energy accumulating element is kept connected to thecapacitive load, V is a final attainment voltage, SR is a slew rate(rate of rise from 10% to 90%) of a waveform of a generated voltage, andy=Ts/(R·Cd).
 44. The apparatus as set forth in claim 43, wherein thefollowing relationship is satisfied: 50(V/μsec)≦V/(R·Cd)*(−0.0002y⁴+0.001y ³+0.009y ²−0.100y+0.386),where Cd is the capacitance of thecapacitive load, R is the resistance value of the charge and dischargepaths of the energy accumulating element with respect to the capacitiveload, the charge and discharge paths including the switching means, Tsis the time during which the energy accumulating element is keptconnected to the capacitive load, V is the final attainment voltage, andy=Ts/(R·Cd).
 45. The apparatus as set forth in claim 42, wherein thefollowing relationship is satisfied: SR≦V/(R·Cd)*(0.0008y ⁴−0.012y³+0.071y ²−0.229y+0.414), when N=3;SR≦V/(R·Cd)*(0.0023y ⁴−0.028y³+0.138y ²−0.336y+0.434), where N=4; andSR≦V/(R·Cd)*(0.0026y ⁴−0.032y³+0.153y ²−0.356y+0.413), where N≧5,where Cd is the capacitance of thecapacitive load, R is the resistance value of the charge and dischargepaths of the energy accumulating elements with respect to the capacitiveload, the charge and discharge paths including the switching means, Tsis the time during which the energy accumulating elements are keptconnected to the capacitive load, V is a final attainment voltage, N isthe number of times each of the energy accumulating elements repeats acharging step during a cycle of a drive pulse, the SR is a slew rate(rate of rise from 10% to 90%) of a waveform of a generated voltage, andy=Ts/(R·Cd).
 46. The apparatus as set forth in claim 45, wherein thefollowing relationship is satisfied: 50(V/μsec)≦V/(R·Cd)*(0.0008y⁴−0.012y ³+0.071y ²−0.229y+0.414), whereN=3;50(V/μsec)≦V/(R·Cd)*(0.0023y ⁴−0.028y ³+0.138y ²−0.336y+0.434),where N=4; and50(V/μsec)≦V/(R·Cd)*(0.0026y ⁴−0.032y ³+0.153y²−0.356y+0.413), when N≧5,where Cd is the capacitance of the capacitiveload, R is the resistance value of the charge and discharge paths of theenergy accumulating elements with respect to the capacitive load, thecharge and discharge paths including the switching means, Ts is the timeduring which the energy accumulating elements are kept connected to thecapacitive load, V is the final attainment voltage, N is the number oftimes each of the energy accumulating elements repeats the charging stepduring the cycle of the drive pulse, and y=Ts/(R·Cd).
 47. The apparatusas set forth in any one of claims 41 through 46, wherein the followingrelationship is satisfied: Cd/Cs≦0.01,where Cs is the capacitivecomponent of the energy accumulating element, and Cd is the capacitanceof the capacitive load.
 48. The apparatus as set forth in any one ofclaims 41 through 47, wherein: the capacitive load is an electrostaticdrive electrode or a piezoid which is provided in an ink-jet head thatpressurizes ink so as to jet out the ink in droplets; and the capacitiveload drive circuit is a drive circuit for driving the electrostaticdrive electrode or the piezoid of the ink-jet head.
 49. An image formingapparatus which includes an ink-jet head that uses an electrostaticdrive electrode or a piezoid as a capacitive load to pressurize ink soas to jet out the ink in droplets, and a drive circuit for driving theelectrostatic drive electrode or the piezoid of the ink-jet head,wherein: the drive circuit is the capacitive load drive circuit as setforth in any one of claims 1 thorough
 36. 50. The image formingapparatus as set forth in claim 49, wherein: the ink-jet head uses thepiezoid to pressurize ink so as to jet out the ink in droplets; and thedrive circuit drives the piezoid of the ink-jet head.
 51. A displayapparatus which includes a display element, and a drive circuit fordriving the display element, wherein: the drive circuit generates apulse to be applied to the display element and collects electrical powerfrom the display element, by using the capacitive load drive circuit asset forth in any one of claims 1 through
 35. 52. A DC-AC converter forgenerating an AC voltage from a single DC voltage, wherein: the drivecircuit generates the AC voltage while collecting electrical power, byusing the capacitive load drive circuit as set forth in any one ofclaims 1 through
 35. 53. A method for driving a capacitive load bycharging and discharging the capacitive load, comprising: anaccumulating step of dividedly accumulating electrostatic energy in aplurality of energy accumulating elements; a charging step ofsequentially supplying the electrostatic energy from the plurality ofenergy accumulating elements to the capacitive load so as to charge thecapacitive load; and a collecting step of discharging the capacitiveload so that the plurality of energy accumulating elements sequentiallycollect the electrostatic energy from the capacitive load.
 54. A methodfor driving a capacitive load by charging and discharging the capacitiveload, comprising: (i) a step of preparing a first energy accumulatingelement having an first initial potential which is not 0, a secondenergy accumulating element, and a reference potential terminal to whicheither (a) a ground potential, (b) a potential which has the samepolarity as the first initial potential supplied from a power source andwhich has a smaller absolute value than the first initial potential, or(c) a potential whose polarity is reverse to the polarity of the firstinitial potential supplied form the power source is applied as areference potential; (ii) an initial potential applying step of applyingthe first initial potential to the first energy accumulating element,and applying to the second energy accumulating element a second initialpotential which has the same polarity as the first initial potential andwhich has a larger absolute value than the first initial potential;(iii) a first charging step of selectively connecting the capacitiveload with the reference potential terminal and then selectivelyconnecting the capacitive load with the first energy accumulatingelement so as to change, toward the first initial potential, a terminalvoltage of the capacitive load; (iv) a second charging step ofselectively connecting the capacitive load with the second energyaccumulating element so as to increase an absolute value of the terminalvoltage of the capacitive load; and (v) a discharging step ofselectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the first charging step, the steps (iii)through (v) being carried out in this order.
 55. A method for driving acapacitive load by charging and discharging the capacitive load,comprising: (i) a step of preparing a power supply terminal to which apower supply potential is applied from a power source, a first energyaccumulating element, and a third energy accumulating element; (ii) aninitial potential applying step of applying to the first energyaccumulating element a first initial potential which has the samepolarity as the power supply potential and which has a smaller absolutevalue than the power supply potential, and applying to the thirdaccumulating element either a potential which has the same polarity asthe first initial potential and which has a smaller absolute value thanthe first initial potential, a ground potential, or a third initialpotential whose potential is reverse to the polarity of the firstinitial potential; (iii) a first charging step of selectively connectingthe capacitive load with the third energy accumulating element and thenselectively connecting the capacitive load with the first energyaccumulating element so as to change, toward the first initialpotential, a terminal voltage of the capacitive load; (iv) a secondcharging step of selectively connecting the capacitive load with thepower supply terminal so as to increase an absolute value of theterminal voltage of the capacitive load; and (v) a discharging step ofselectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the first charging step, the steps (iii)through (v) being carried out in this order.
 56. A method for driving acapacitive load by charging and discharging the capacitive load,comprising: (i) a step of preparing a first energy accumulating element,a second energy accumulating element, and a third energy accumulatingelement; (ii) an initial potential applying step of applying to thefirst energy accumulating element a first initial potential which is not0, applying to the second energy accumulating element a second initialpotential which has a larger absolute value than the initial potentialof the first energy accumulating element, and applying to the thirdaccumulating element either a potential which has the same polarity asthe first initial potential and which has a smaller absolute value thanthe first initial potential, a ground potential, or a third initialpotential whose potential is reverse to the polarity of the firstinitial potential; (iii) a first charging step of selectively connectingthe capacitive load with the third energy accumulating element and thenselectively connecting the capacitive load with the first energyaccumulating element so as to change, toward the first initialpotential, a terminal voltage of the capacitive load; (iv) a secondcharging step of selectively connecting the capacitive load with thesecond energy accumulating element so as to increase an absolute valueof the terminal voltage of the capacitive load; and (v) a dischargingstep of selectively connecting the capacitive load with the first energyaccumulating element so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelement, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating element before the first charging step, the steps (iii)through (v) being carried out in this order.
 57. A method for driving acapacitive load by charging and discharging the capacitive load,comprising: a providing step of preparing a power supply terminal towhich a power supply potential is applied from a power source, areference potential terminal to which either a reference power supplypotential supplied from a reference power source which is different fromthe power supply potential or a ground potential is applied as areference potential, and a plurality of first energy accumulatingelements; an initial potential applying step of respectively applying tothe plurality of first energy accumulating elements initial potentialswhich are different from one another and which are between the referencepotential and the power supply potential; and steps of (1) connectingthe capacitive load with the reference potential terminal and thensequentially connecting the capacitive load with the first energyaccumulating elements in an order of the initial potentials from theinitial potential closest to the reference potential, so as to change,toward the power supply potential, a terminal voltage of the capacitiveload, (2) selectively connecting the capacitive load with the powersupply terminal so as to increase an absolute value of the terminalvoltage of the capacitive load, and (3) selectively connecting thecapacitive load with the first energy accumulating elements in an orderof the initial potentials from the initial potential closest to thepower supply potential, so as to decrease the absolute value of theterminal voltage of the capacitive load and so as to regenerateelectrostatic energy to be accumulated in the first energy accumulatingelements, the thus regenerated electrostatic energy being approximatelyequal to electrostatic energy as accumulated in the first energyaccumulating elements before the step (1), the steps (1) through (3)being carried out in this order.